Pacific ENSO Update

1st Quarter 2002-Vol. 8 No. 1


CURRENT CONDITIONS

    A major shift in the tropical western Pacific wind patterns commenced during December 2001; when strong westerly winds became established for much of the month in the equatorial latitudes (5N-5S) (Figure 1).  Westerly winds of near gale force pushed eastward along the equator and reached the islands of western Kiribati on December 13.  This marked the farthest eastward penetration of low-latitude westerlies in the western Pacific since December 1997.  The equatorial westerly winds of December in the western Pacific were associated with one of Micronesia’s most unusual tropical cyclones, Super Typhoon Faxai (31W).

    The persistent December low-level westerly winds at low latitudes in the western Pacific are a major change to the wind pattern that has been anomalously easterly since 1998.  As December came to a close, the band of low-latitude westerly winds shifted to the Southern Hemisphere, and extended east of the Date Line to the large Tropical Cyclone “Waka” that affected Samoa.  The return of strong westerly winds to the equatorial latitudes of the western North Pacific may act to set the stage for the next El Niño event; one that could begin as early as April 2002.  An El Niño event in 2002 would cause heavier rains in the spring and summer throughout Micronesia that would give way to drier than normal conditions late in 2002 and into early 2003.  An El Niño event in 2002 could also bring an increased threat of tropical cyclones to Guam, Saipan, Phonpei and Kosrae States, and to the RMI.

     The U.S. Climate Prediction Center released the following statement on 09 January 2002 (in part):

    “… The latest statistical and coupled model predictions show a spread ranging from near-normal to moderate warm episode conditions [El Niño] over the next 3-6 months.  … Considering the observed oceanic and atmospheric circulation patterns and their recent evolution, it seems most likely that warm-episode conditions [El Niño] will develop in the tropical Pacific during the next 3-6 months.  …”

    Definitions of El Niño developed in the early 1980s were contingent on persistent SST anomalies of at least +1ºC along the tropical Pacific coast of South America, while more recent definitions have focused on persistent SST anomalies of at least +0.4ºC in the central equatorial Pacific.  At this time, it is too early to accurately predict when central equatorial Pacific SST anomalies, along with other climate indicators, will become large enough for sufficient time to declare the next El Niño event.  The tropical Pacific SST distribution and the slightly negative values of the SOI remain indicative of El Niño-neutral conditions; however, the dramatic change of the equatorial Pacific winds, and tropical cyclone activity in eastern Micronesia and near Samoa hint at the arrival of the next El Niño in 2002.  It should be clear by April of 2002 whether or not El Niño has begun.

Look for the following climate anomalies if El Niño begins within the next three to five months:

(1) a warming of the SST in the central and eastern Equatorial Pacific,
(2) a fall of the SOI to persistently negative values near –0.5 or lower,
(3) a continuation of episodes of westerly winds near, and south of, the equator during January through March in association with tropical cyclones in the South  Pacific from the Northeast Australian coast eastward to the Fiji Islands, and from there, southeastward  into French Polynesia
(4) an early development in late March or April of the near equatorial trough and the arrival of westerly monsoonal winds in Chuuk and Pohnpei States,
(5) the formation of “early season” tropical cyclones in the Caroline islands occurring from mid-March through June, and
(6) a fall in the sea level heights, beginning in western Micronesia and propagating eastward and southward.

SST

    Sea surface temperatures (SSTs) across the tropical Pacific are within 0.5ºC of normal, with a distribution of slightly warmer than normal SSTs in the western and central equatorial Pacific, and slightly cooler that normal SSTs in the eastern equatorial Pacific from south of Hawaii to the coast of South America.  This situation may change by late January or early February as the ocean responds to December’s persistent westerly wind flow along the equator in the western Pacific with warming of the SST in the areas of the eastern equatorial Pacific that are now slightly colder than normal.

     The depth of the equatorial oceanic thermocline (as represented by the depth of the 20°C isotherm) continued to remain deeper than normal in the western Pacific and near normal in the extreme eastern Pacific.  The temperature of the sub-surface ocean water is generally at least 1.0ºC warmer than normal to a depth of 250 meters in the equatorial western Pacific, eastward to the longitude of Hawaii (~155W).  Peak warm anomalies at depth occur near 170E, where the temperature at 150 meters is over 4ºC warmer than normal.  The sub-surface waters of the eastern equatorial Pacific remain cooler than normal from 135W, eastward to the coast of South America.  A gradual eastward expansion of warmer than normal sub-surface water is expected as the ocean responds to December’s westerly wind along the equator.  An eastward shift of warmer than normal sub-surface water would be another indicator of the start of El Niño in 2002.

SOI

   The Southern Oscillation Index (SOI) has averaged near zero for the last six months with month-to-month swings into positive and negative values:  August (-1.0), September (+0.2), October (-0.4), November (+0.7), and December (-1.2).  The SST distribution in the tropical Pacific and the status of the SOI are still indicative of a climate state that is neither El Niño nor La Niña (designated by some as “El Niño-neutral”).  The major December westerly wind episodes, however, mark a significant change in the regional climate, and could be a precursor to the next El Niño.

    If El Niño begins in 2002, the SOI may drop to persistent negative values of –0.5 or lower for most of the year.  With the SOI in weak to moderate negative territory, atmospheric circulation patterns should exhibit patterns that are consistent with El Niño.  This includes westerly monsoonal winds extending eastward to near the Fiji Islands in January through March, then an early onset of westerly monsoonal winds in Micronesia in late March or April.

TROPICAL CYCLONE ACTIVITY

    Western North Pacific tropical cyclone activity from October through December 2001 included 7 tropical cyclones - Krosa, Haiyan, Podul, Lingling, Kajiki, Faxai and Vamei- named by the Japan Meteorological Agency (JMA). The Joint Typhoon Warning Center (JTWC) identified 9 total tropical cyclones, including Tropical Storm 28W and Tropical Storm 29W in addition to those named by the JMA.  All but two of the tropical cyclones (Tropical Storm 28W and Typhoon Vamei) had some effect on the islands of Micronesia.  Typhoon Krosa and Tropical Storm 28W formed near Guam; Super Typhoon Podul and Super Typhoon Faxai formed near Pohnpei; and the tropical disturbances that became Typhoons Haiyan, Lingling, and Kajiki provided rainfall to western parts of Micronesia before they moved westward toward the Philippines and intensified.  The northern Mariana Islands, Pohnpei, and Kosrae were directly affected by tropical cyclones occurring from October through December.  On the night of October 03, the tropical depression that became Typhoon Krosa passed south of Saipan and Tinian bringing heavy rain and gusty winds to those islands.  An intense thunderstorm that caused damaging floods on Guam on October 14 was loosely associated with the tropical disturbance that became Super Typhoon Podul.  This tropical disturbance consolidated into a tropical depression when it was near Pohnpei on October 19. It later moved north and became a super typhoon.  Pohnpei experienced some heavy rain and gusty winds but no reports of injury or damage were received.  The monsoon depression that became Typhoon Lingling moved south of Guam on November 04 bringing widespread heavy rains of 2-3 inches.  Two days of heavy rain on Guam (17 and 18 November) were associated with a tropical depression that became Tropical Storm 28W.  The tropical depression that became Typhoon Kajiki passed to the south of Guam on the night of 02 December, bringing heavy rain to the southern villages and a spectacular display of lightning offshore to the south.  It drifted westward toward the Philippines, and produced heavy showers over Palau on 04 December.

    In mid-December, one of Micronesia’s most unusual tropical cyclones of record, Super Typhoon Faxai, consolidated in the eastern Caroline Islands.  Faxai (A Laotian name pronounced “Fahs-eye”) became a numbered tropical depression (TC 31W) near Pohnpei on December 12, and then moved eastward toward Kosrae and intensified to a tropical storm.  For several days, Faxai (as a tropical storm) remained within 100 miles of Kosrae, providing very heavy rains, gusty winds, and high surf that caused some damage from inundation of coastal homes.  After stalling near Kosrae, Faxai finally moved on a recurving track where it pass to the northeast of Guam and Saipan.  This was fortunate since its intensity climbed to an extremely high value of 160 kt (185 mph) sustained wind with gusts to 195 kt (225 mph).  As it moved northward into higher latitudes, Faxai swiped the Island of Agrihan on December 24, with typhoon force winds that caused some damage to the vegetation and to a few of the residential houses there.

    Based on an expectation of El Niño in 2002, a near normal number of tropical cyclones in the western North Pacific is anticipated for 2002.  However, during El Niño, the region of formation of tropical cyclones shifts eastward into the eastern Caroline Islands and the RMI.  The risk of tropical cyclones for Guam, the CNMI, the eastern Caroline Islands, and the RMI is increased during an El Niño year.  Also, during an El Niño year, tropical cyclone activity gets off to an early start with an increased number of tropical cyclones in the “Early Season” period of Mid-March through June.  Thus, as early as March or April, tropical depressions may form in Pohnpei and Kosrae States and in the RMI.  One or two of these tropical depressions could become typhoons as they move northward out of the FSM and may threaten Guam and the CNMI as full-fledged typhoons.

NOTE:   During late December, American Samoa narrowly missed a direct hit by the large Tropical Cyclone Waka.  Cyclone Waka caused heavy rain and brought strong north winds that gusted to 56 mph at Pago Pago.  Damage was restricted to some downed banana trees and broken twigs and branches of vulnerable trees. 


 NOAA's Climate Prediction Center in Washington D.C. routinely monitors the lastest forecast results from several ENSO models. The prognostic discussion for long-lead outlooks outlines these results. 
LOCAL VARIABILITY SUMMARIES (2001 IN REVIEW)

State of Hawaii:  A very dynamic month for weather with the occurrence of 3 cold fronts, 2 upper level systems, and a significant kona low. The Hawaiian Islands began the year within a pattern of persistent low level southwesterlies that started during the middle of December 2001. A series of weak cold fronts pushed across the state on 3, 6, and 9 January though with little associated rainfall. Trade winds did not resume until 14 January.

     On 19 January, an upper level low arrived over the eastern side of the Hawaiian Islands marking the start of a very wet weather pattern. The upper level low was superimposed over fresh to strong low level trade winds and helped trigger thunderstorms and heavy showers over the windward portions of the Big Island and Maui. No flooding problems were reported during this event.

     An upper level trough southwest of the state began to affect island weather on 24 January. Initially, its effects were mainly in the form of overcast skies beneath moderate trades. However, orographically anchored heavy showers developed during the late afternoon of 26 January over the windward slopes of O'ahu, Maui, and the Big Island. Heavy rains also occurred in the leeward Kohala area of the Big Island. Rainfall was heaviest over the Ko'olaus of O'ahu. Stream flooding in Honolulu swept 3 boys down a drainage canal. All 3 were successfully rescued. The heavy rains and stream flooding also stranded 3 hikers on Oahu mountain trails overnight. All 3 walked out the following morning. Unfortunately, heavy rains over the windward slopes of the West Maui Mountains resulted in 3 fatalities. These individuals were among 5 passengers in a vehicle that attempted to cross a fast flowing stream near Waiehu, Maui. Flood damage to secondary roads was also noted in leeward Kohala.

    Lastly, a kona low developed west of Kaua'i bringing heavy rains across the state from 28 to 30 January. The heaviest rains occurred on 29 January with flooding reported over east O'ahu, Moloka'i, Maui, Lana'i, and the Big Island. The highest rainfall totals were from gages in the Ka'u and Hilo sections of the Big Island (see discussion in Big Island section below for more details). However, the most significant damage was on the island of Lana'i where 10 luxury homes at Manele were inundated by as much as 4 feet of water. Fortunately, no fatalities or significant injuries were reported. Two individuals required rescue on the Big Island north of Hilo when their vehicle became stranded in a low water crossing flooded by a swollen stream.

Kevin Kodama-Senior Service Hydrologist, NWSFO Honolulu, Hawaii


For a more complete summary, and the county by county wrap-ups, please see the January 2002 Precipitation Summary from the National Weather Service Honolulu Weather Forecast Office. 

American Samoa:  Rainfall at Pago Pago Airport for October, November, and December was 8.80 inches (82%), 8.54 inches (79%), and 15.77 inches (101%), respectively, amounting to 89% of normal for the 3-month period.  During 2001, only the months of February, March, and December 2001 had above average monthly rainfall.  The rains of February and March 2001 accompanied several active periods of the northwest monsoon.  December’s rain was enhanced by the near passage of the large Tropical Cyclone Waka. All other months of 2001 were drier than average, yielding an annual total of 96.83 inches.  The 2001 annual total fell quite a bit short (79%) of the normal 121.80 inches Figure 2.

    Rainfall in American Samoa is not as closely tied to ENSO as it is in other regions of the Pacific.  Some prolonged very dry periods (1982-83, 1987, 1990, 1993, and 1998) at American Samoa have occurred in association with major El Niño events (years shown in bold type), and some prolonged very wet periods (1980-81, 1985-86, 1994, and 1999) have occurred in years prior to major El Niño events (years shown in bold type).  However, there is not a consistent ENSO signal in the rainfall there on average.  There is a tendency for American Samoa to experience prolonged dry periods in the years following intense El Niño events, such as 1997-98, and to be wet during weak to moderate El Niño years.  Thus, while El Niño is now anticipated to commence during 2002, it is unknown how intense this El Niño might be.  Historically, El Niño years have near-normal rainfall, so the outlook for American Samoa for all of 2002 is for near-normal rainfall.  If a very intense El Niño develops during 2002, then a prolonged dry period may commence in early 2003.

    With the expected onset of El Niño in 2002, the risk of a damaging tropical cyclone increases for American Samoa. There is a chance that another cyclone like Waka will menace the Samoa Islands from January through March 2002, and a then a greater threat may occur in a year’s time from December 2002 through March 2003.

Predicted rainfall for American Samoa from January 2002 through December 2002 is:
 
 Inclusive Period
% of long-term average
Jan 2002-Jun 2002
100%
Jul 2002-Dec 2002
 90%
(source: UOG-WERI)

Guam/CNMI:  Rainfall at Guam International Airport (GIA) during October, November, and December was 11.48 inches (95%), 12.99 inches (158%), and 6.21 inches (115%), respectively.  This amounted to 120% of the normal value for the period October-December.  Andersen Air Force Base (AAFB) measured 13.09 inches (102%), 13.34 inches (147%), and 9.51 inches (159%), or 120% of the average rainfall for October-December.  A relatively wet autumn capped off a year that saw a near-normal annual rainfall at most locations on Guam (Figure 2).  The GIA 2001 annual total was 103.27 inches (114%), and the AAFB 2001 annual total was 98.61 (100%).  The months of January through May were very dry on Guam.  Then during June, the dry season came to an abrupt end as island thunderstorms occurred throughout the month.  August was very wet as monsoon southwesterlies dominated the weather pattern with many days of heavy rains and gusty monsoon squalls.  The monsoon became inactive in September and Guam was dry.  Then, from October through December, some tropical disturbances passed near Guam, causing several periods of heavy rainfall.  An extreme rain event of 4-6 inches in only a few hours occurred on Guam on October 14.  Extensive flooding of homes in the central part of the island caused millions of dollars of personal property damage.  Lightning strikes temporarily knocked out power (see the discussion of Tropical Cyclones).  Later, in November and December, several shear line passages also contributed substantial precipitation.  On December 31, the year ended with a shear line dropping southward over the island and producing a half-inch of rain before midnight of the New Year.  An additional half-inch of rain fell before sun-up of the first day of 2002.   There was no direct passage of a tropical cyclone over Guam in 2001, although some tropical disturbances (some of which later became typhoons in the Philippine Sea) passed by the island.

    October, November, and December rainfall at the Saipan International Airport (SIA) was 7.43 inches (69%), 4.01 inches (69%), and 3.19 inches (64%), or only 72% of the average for the period.  For the same months, Capitol Hill’s measured rainfall was 8.70 inches (73%), 10.64 inches (146%), and 5.95 inches (124%) respectively.  Thus, at Capitol Hill, quarterly rainfall was somewhat higher at 105%.  Only during August when strong monsoon flow persisted in the southern Marianas, did the SIA receive substantially higher than normal rainfall. Otherwise, most months were dry at the SIA and the annual total was 62.44 inches (84%). The SIA was the driest location reporting rainfall on Saipan during 2001.  At Capitol Hill there was much more rainfall than at the SIA with October through December receiving a three-month total of 25.29 inches (105%).  The 2001 annual total of 93.71 inches at Capitol Hill was 112% of normal.  Other locations on Saipan had 2001 annual rainfall totals on the order of 70-80 inches, which was slightly drier than normal to near normal.

     Rainfall amounts for October, November, and December at the Tinian Airport were 11.18 inches (98%), 8.01 inches (110%), and 5.70 inches (119%), respectively. The 3-month rainfall for Tinian Airport was above normal at 106%.  The 2001 annual total of 80.97 inches at the Tinian airport was near normal (97%).  At Rota Airport, October, November, and December rain amounts were 9.33 inches (74%), 13.77 inches (159%), and 5.45 inches (96%), respectively. This gave a 3-month average of 106%.  On the northern part of Rota, at the beautiful Rota Resort and Country Club, the NASA TRMM network there recorded a bit less rainfall than at the airport for the period October-December.

    Based on 30 years of rainfall data, El Niño years on Guam and the CNMI average slightly wetter than normal.  This should be expected since monsoon and tropical cyclone activity are normally greater during these years.  Guam’s wettest year of record (1976) was an El Niño year.  The extreme rainfall of that year was, in large measure, a result of the near passage of many tropical disturbances and tropical cyclones, and a direct hit by Typhoon Pamela in May.  A recent El Niño year, 1997, was also very wet, in large measure due to the rains from Super Typhoon Paka, and an extremely wet southwest monsoon during most of August.

     The very dry conditions that follow an El Niño year tend to start in November and carry 4-7 months into the year following El Niño.  An El Niño event is now anticipated to begin in 2002; however, it is still too early to predict whether it will be a weak, moderate or strong event.  An El Niño event in 2002 would likely produce slightly greater than average rainfall overall in Guam and the CNMI during this forecast period, with persistent dryness beginning late in the year.  During March through June 2002, an early start of tropical cyclone activity is expected, with possible typhoon threats in April or May.  The typhoon threat should remain slightly elevated for the remainder of the year, with September through November being the months of greatest threats.  Most of these will approach from the east-southeast.

Predicted rainfall for the Mariana Islands is as follows:
Inclusive Period 
% of long-term average 
- - -
Guam/Rota                     Saipan/Tinian
   Jan 2002-Oct 2002
105%                              100%
Nov 2002-Dec 2002
95%                                90%
Jan 2003-Jun 2003 
80%                                75%
 *Unless a tropical cyclone passes near the island
(source: UOG-WERI)
 

Yap State:  Drier than average conditions dominated most of Yap State during the months of October, November, and December, with quite high month-to-month variability.  During October-December, several tropical disturbances passed near Yap State producing episodes of heavy showers.  In late November and December, a few shear lines pushed as far south as Yap, contributing a significant portion of the total rainfall.  The weather station at the Yap Airport recorded 7.33 inches (61%) in October, 7.56 inches (83%) in November, and 11.99 inches (133%) in December, or 90% of normal rainfall for the three months.  October, November, and December rainfall amounts on Ulithi were 10.08 inches (94%), 8.46 inches (110%), and 6.30 inches (82%) or 95% for the 3-month period. Farther south at Woleai Atoll, rainfall was 7.74 inches (57%) in October, 8.11 inches (75%) in November, and 11.89 inches (104%) in December, for a 3-month average of 77%.  Overall in 2001, Yap State was near average (Figure 2) with 2001 annual totals of 120.50 inches (100%), 115.47 inches (113%), and 130.95 inches (94%) at Yap Airport, Ulithi, and Woleai, respectively.  July and August were particularly wet at Yap State, the result of an active southwest monsoon and several near passages of tropical disturbances that later moved northwest and became named tropical cyclones.

    El Niño years at Yap average slightly wetter than normal.  This should be expected since monsoon and tropical cyclone activity are normally greater during these years.   The very dry conditions that follow an El Niño year tend to start in November and carry into the year following El Niño.  An El Niño event is now anticipated to begin in 2002; however, it is still to early to predict whether it will be a weak, moderate, or strong event.  An El Niño event in 2002 would likely produce slightly greater than average rainfall overall in Yap during this forecast period, with persistent dryness beginning late in the year.  During March through June, an early start of tropical cyclone activity is expected, with possible typhoon threats in April or May.  The typhoon threat should be near normal for the remainder of the year, with September through November being the months of greatest threats.

Predicted rainfall for Yap State is as follows:
Inclusive Period
% of long-term average
- - -
                 Yap Island                       Outer Atolls: 
- - -
                                               S. of 8ºN   N. of 8ºN
 Jan 2002-Sep 2002
105%                        115%         100%
Oct 2002-Dec 2002
90%                          85%           90%
Jan 2003-Jun 2003
 80%                          80%            80%
(source: UOG-WERI)
 

Chuuk State:  During October, November, and December, the weather station at Weno Island measured 15.11 inches (113%), 11.66 inches (113%), and 7.92 inches (73%).  This amounted to 100% of normal amounts for the 3-month period.  The wet conditions of October and November were the result of showers and thunderstorms in the near- equatorial trough and the passages of tropical disturbances.  December was dry overall because of a prolonged dry period when Tropical Storm Faxai moved eastward and stalled near Kosrae, choking off the rainfall in the islands of the FSM south of 10N and west of Pohnpei.  Overall during 2001, Weno was slightly drier than normal (Figure 2).  The 2001 annual total of 128.11 inches was 95% of normal.  In the Mortlocks at Lukunoch, rainfall for October, November, and December was 8.65 inches (64%), 11.65 inches (113%), and 11.60 inches (107%) for the respective months.  The 3-month average was 92%.  The 2001 annual total for Lukunoch was 126.11 (94%).  Many of the islands of Chuuk State experienced a prolonged period of dryness from July through September.  Satellite imagery confirms a sharp decrease (especially during September) in shower and thunderstorm activity associated with a weak ridge of high pressure that stretched through the Caroline island groups bringing periods of clear, hot, and dry conditions to Palau, Chuuk, Pohnpei, and Kosrae.

    Rainfall for all of Chuuk State is expected to be wetter than normal as the monsoon trough moves back into the region by April.  High month-to-month variability is possible whenever rainfall is produced by an active monsoon.  Tropical cyclone activity may begin in April or May with the early onset of the monsoon trough.  The tropical cyclone threat should be normal in Chuuk State for the second half of 2002.  Most of the tropical cyclones near Chuuk will be the precursor tropical disturbances that will form or move near Chuuk and later move northwest to become tropical cyclones.  Chuuk will have a chance of getting a tropical storm, primarily during the months of April and May.

Predictions for Chuuk State are as follows:
 
Inclusive Period
% of long-term average 
- - -
       Chuuk                         Outer Atolls: 
- - -
      Lagoon               Southern/Western   Northern
Jan 2002-June 2002 
        110%                            110%               100%
July 2002-Dec 2002
         95%                              95%                 95%
Jan 2003-Jun 2003 
         85%                              85%                 85%
(source: UOG-WERI)
 

Pohnpei State:  Rainfall at Pohnpei State was generally wetter than normal for the three-month period October-December.  The near-equatorial trough and tropical disturbances traveling westward along it were responsible for much of the rainfall.  Podul (as a tropical storm) and Faxai (as a tropical depression) were responsible for heavy rains in much of Pohnpei State in October and December, respectively.  At the weather station at Kolonia, the October, November, and December rainfall totals were 17.48 inches (105%), 14.47 inches (92%), and 18.56 inches (122%), respectively.  This amounted to a 3-month value of 106% of average precipitation.  At Pingalap, observed rainfall in October, November, and December was 22.83 inches (154%), 10.76 inches (76%), and 24.56 inches (184%), respectively, for a 3-month amount of 137%.  At Nukuoro, October through December precipitation amounts were 13.22 inches (123%), 10.64 inches (89%), and 6.28 inches (52%), respectively.  Kapingamarangi was much wetter than normal, as convection in persistent equatorial westerly wind flow produced abundant rains.  October, November, and December rainfall measurements there were 13.30 inches (276%), 8.03 inches (98%), and 13.97 inches (160%) respectively.  This followed a wet April-September that had a 6-month average of 159%.  Overall in 2001, most islands of Pohnpei State were drier than normal (with a notable exception of Kapingamarangi).  The 2001 annual totals at Kolonia, Pingelap, Nukuoro, and Kapingamarangi were 174.21 inches (92%), 158.48 inches (89%), 173.04 (116%), and 142.66 inches (130%) respectively.  Many of the islands of Pohnpei State lost ground during a hot dry spell during July-September.  Convection along the equator and enhanced monsoonal westerlies there in October-December, kept Kapingamarangi in rainfall surpluses for almost every month of 2001.

    Rainfall for all of Pohnpei State is expected to be wetter than normal as the monsoon trough moves back into the region by April.  High month-to-month variability is possible whenever rainfall is produced by an active monsoon.  Tropical cyclone activity may begin in April or May with the early onset of the monsoon trough.  The tropical cyclone threat should be normal in Pohnpei State for the second half of 2002.  Most of the tropical cyclones near Pohnpei will be the precursor tropical disturbances that will form or move over Pohnpei, and later move northwest and become tropical cyclones.  Pohnpei will have a chance of getting a tropical storm, primarily during the months of April and May.

    El Niño years at Pohnpei average slightly wetter than normal.  This should be expected since monsoon and tropical cyclone activity are normally greater during these years.   The very dry conditions that follow an El Niño year tend to start in November and carry into the year following El Niño. An El Niño event is now anticipated to begin in 2002; however, it is still to early to predict whether it will be a weak, moderate, or strong Event.  An El Niño event in 2002 would likely produce slightly greater than average rainfall overall in Pohnpei during this forecast period, with persistent dryness beginning late in the year.  During March through June, an early start of tropical cyclone activity is expected, with possible typhoon threats in April or May.  The typhoon threat should be near normal for the remainder of the year, with September through November being the months of greatest threats.

Predicted rainfall for Pohnpei State is as follows:
 
Inclusive Period 
 % of long-term average 
- - - 
       Pohnpei                             Outer Atolls 
- - -
       Island                    Eastern   Southern  Equatorial
Jan 2002-Sep 2002
110%                      110%     110%      110%
Oct 2002-Dec 2002
95%                        100%      95%        95%
Jan 2003-Jun 2003
85%                         85%       85%        75%
(source: UOG-WERI)

Kosrae State:  Rainfall at Kosrae was near normal during October and November with 15.50 inches (96%) and 16.70 inches (105%) respectively.  December, however, was extremely wet with 42.57 inches (294%).  Much of the tremendous amount of rainfall in December occurred when a tropical cyclone, Faxai, stalled near the island for several days.  Damage to personal property was caused by coastal inundation from large waves and by flooding from heavy rains.  The following excerpts from the Kaselehlie Press (Vol. 2, Issue No. 3, December 27, 2001.  Byline Olivier Wortel) describes the effects of Faxai:

    “With power outages and fish flopping in living rooms, people quickly mobilized to assess the damage and help each other in the aftermath of the first tidal surge Kosrae has seen in at least a decade. … Heuston Waguk, [Police officer on duty, and resident of Utwe on the southwest side of Kosrae, reported:] … ‘We came straight to Utwe…I saw the waves coming on the road with all kinds of rocks and gravel, it was like a river.  Two or three waves coming at one time … First time in my life that the waves came up and into my house … All our crops beside the house, breadfruits, lemon tress, sugarcanes, have turned brown from the saltwater, my wife even found a reef fish drifting inside the house …’.   On Thursday, December 13th, with Tropical Depression 31-W circling 65 nautical miles west of Kosrae, gusting winds and torrential rains battered the island, culminating in an awesome display of tin-rattling thunder claps and pink spears of lightning over the Finkol valley.  By Friday morning the rivers were swollen and raging.  Malem Elementary School was flooded with water and mud …  Tofol, where all the government offices are, and a natural flood plain situated between the highest peaks of Kosrae – Mounts Finkol, Mutunte, and Wakaap – was one big reservoir of mud, hibiscus and banana tress, and water.  Two feet of mud and water pushed against and into the Education Department, the High School classrooms, the Peace Corps lounge and office, the Upward Bound Office, the Bank of Hawaii, and other government buildings.  … workers spent the day cleaning and mopping and salvaging what they could.  …”

    Kosrae was somewhat dry for several months during the summer when a weak ridge of high pressure stretched through the Caroline island groups bringing clear, hot, and dry conditions to Palau, Chuuk, Pohnpei, and Kosrae.  December’s cloudbursts, however, helped to bring the annual total above normal.  The 2001 annual totals at Kosrae (SAWRS), Utwe, Tafunsak, and Tofol were 217.68 inches (106%), 195.07 inches, 204.99 inches, and 224.37 inches, respectively.

    Rainfall for Kosrae is expected to be above normal from January through October, and then below normal for the remainder of the forecast period.  However, high variability should be expected in the month-to-month rainfall amounts.  If El Niño begins in 2002, some tropical disturbances will form near Kosrae in April or May that later move northwest and become named tropical cyclones.  There is a slight risk that Kosrae could experience one or two periods of rough seas and heavy rains with strong westerly winds from developing tropical cyclones passing to the north during April and May 2002, and then again during September through November 2002.  Dry conditions associated with El Niño may begin in early 2003.

Predicted rainfall for Kosrae State is as follows:
 
Inclusive Period 
% of long-term average
- - - 
Kosrae State
Jan 2002-Sep 2002 
110%
Oct 2002-Dec 2002
95%
Jan 2003-Jun 2003
85%
(source: UOG-WERI)

Republic of Palau:  Rainfall at Koror during October, November, and December was 14.48 inches (104%), 11.69 inches (103%), and 15.76 inches (132%), respectively.  The 3-month average was 113% of normal.  For 4 months in a row (June-August), Koror received more than 20 inches of rain per month; then, in September, the island experienced a dry break.  In October through December, abundant rains returned to Palau as several tropical disturbances (some of which later became named tropical cyclones) passed over or near the island group.  For the 3-months of October, November and December, the monthly rainfall distribution at Nekken Forestry was a bit drier than at the airport with 9.67 inches, 10.37 inches, and 14.88 inches respectively.  Farther south at Peleliu, conditions were wetter overall, with 10.11 inches in October, 17.30 inches in November, and 20.16 inches in December.  The 2001 annual total at Nekken Forestry was 154.13 inches, and at Peliliu it was 154.85 inches – each a bit drier than at Koror where the annual total was 168.33 inches (114%).

    An El Niño event is now anticipated to begin in 2002; however, it is still to early to predict whether it will be a weak, moderate, or strong event.  El Niño years at Palau average wetter than normal through September, then dry conditions set in for an extended period.  The very dry conditions that follow an El Niño year tend to start in October and carry into the year following El Niño.  During March through June, an early start of tropical cyclone activity is expected in the western North Pacific, with possible tropical storm threats to Palau in April, May, or June.  The tropical cyclone threat should be near normal for the remainder of the year, with September through November being the months of greatest threats.

Predicted rainfall for Palau is as follows:
 
Inclusive Period 
% of long-term average
- - -
     Koror and                         Outer Atolls:
- - - 
   Mountain Is                  N. of 8ºN       S. of 8ºN
Jan 2002-Sep 2002
      110%                              105%            105%
Oct 2002-Dec 2002
       95%                                90%              90%
Jan 2003-Jun 2003 
       85%                               80%               80%
(source: UOG-WERI)

Republic of the Marshall Islands (RMI):  Quite dry conditions dominated the Republic of the Marshall Islands (RMI) during the first half of 2001, and continued to dominate the northern islands during July through September.  The Majuro weather station (representative of the southern islands) measured 20.19 inches (146%), 14.92 inches (117%), and 9.02 inches (76%) during October, November, and December, respectively.  For the 3-month period, the average for Majuro was 115%.  At nearby Laura the net rainfall amount for October, November, and December (39.49 inches) was just a little bit drier than at Majuro.  Rainfall at Kwajalein (and nearby Ebeye) was 15.52 inches (130%) in October, 13.70 inches (129%) in November, and 7.96 (98%) inches in December.  Kwajalein (representative of the central islands) was dry in 2001 in every month from January to September, with just over half (54%) of normal rainfall for the 9-month period.  The only months with over 10 inches of rain at Kwajalein were October and November when convection associated with tropical disturbances in the tradewind trough pushed northward.  The 2001 annual total at Kwajalein was only 75.84 inches, or 74% of normal (Figure 2).

    Alingalaplap continued to be drier than Majuro with 5.65 inches in October, 6.63 inches in November, and 3.16 inches in December.  Both Jaluit and Majuro were very wet in September and October, but a bit drier than average during the other months of 2001.  Jaluit was only slightly drier then Majuro overall in 2001 (Figure 2).  Farther north, Wotje continued to be the driest of the locations in the RMI that measured rainfall.  The accumulated rainfall at Wotje for the three-month period October through December was less than 20 inches.  The values of rainfall in the northern islands of the RMI were low for most of 2001; this was supported by satellite imagery showing most of the rainfall confined to showers along the trade wind trough, which tended to be south of these islands.

    An El Niño event is now anticipated to begin in 2002; however, it is still to early to predict whether it will be a weak, moderate, or strong event. Rainfall during El Niño years in the RMI averages near normal, then dry conditions set in for an extended period in the first 4-6 months of the year following El Niño.  During March through June, an early start of tropical cyclone activity is expected in the western North Pacific, with possible development of tropical disturbances in the RMI that later move west and become named tropical cyclones.  The tropical cyclone threat should be slightly elevated for the remainder of the year, with October through December being the months of greatest threats when the monsoon trough extends eastward into the RMI.

Predicted rainfall for the RMI  is as follows:
 
 
Inclusive Period
% of long-term average
- - -
   Southern         Central           Northern 
- - -
   Islands             Islands             Islands
Jan 2002-Sep 2002
     105%                105%                100%
Oct 2002-Dec 2002
     95%                   95%                 90%
Jan 2003-Jun 2003
     85%                    85%                 80%
(source: UOG-WERI)


APPENDICES:

ENSO ADVISORY:  issued by Climate Prediction Center/NCEP on March 7, 2002

    The evolution towards a warm episode in the tropical Pacific continued during February 2002. Warmer-than-normal sea surface and subsurface temperatures developed throughout the equatorial Pacific during the month. By late in the month equatorial SST anomalies exceeded +1°C from 165°E to 180 °W, and in the extreme eastern equatorial Pacific near the South American coast. The warming of surface and subsurface waters along the South American coast was due to the arrival of the oceanic Kelvin wave that has been propagating eastward from the central equatorial Pacific since mid-December. These conditions are often observed in the early stages of El Niño.

    Several of the atmospheric indices indicate that El Niño/ Southern Oscillation (ENSO) conditions have not developed to the point that guarantees sustained growth of the event. Those indices include the Southern Oscillation Index (Tahiti-Darwin SOI), and both lower-tropospheric and upper-tropospheric wind indices. [Note, these indices are often inconsistent in the early stages of El Niño, and that they develop El Niño characteristics as the event evolves.] In contrast, enhanced rainfall has been observed over the tropical west-central Pacific, from Papua New Guinea eastward to the date line (180°W) since the beginning of 2002. Enhanced rainfall also developed in late February over the warmer-than-normal waters between the west coast of South America and the Galapagos Islands. These features reflect the warming in the sea surface temperatures, and are possibly the first atmospheric effects of a developing El Niño.  The latest statistical and coupled model predictions show a spread from slightly cooler-than-normal conditions to moderate warm-episode conditions during the remainder of 2002. The coupled models and some statistical techniques that incorporate subsurface oceanic conditions indicate a slow evolution to weak or moderate warm-episode (El Niño) conditions during the next several months. Other techniques indicate that conditions will remain near normal or even return to slightly colder than normal for the remainder of 2002. The recent evolution in oceanic conditions supports the forecasts of a continued evolution toward El Niño.

SPECIAL SECTION-Markov Model for Pacific SST and sea level

    These are the latest results of a  CPC model being produced by Dr. Yan Xue.  Forecasts of the tropical Pacific SST and sea level anomalies are presented here using a linear statistical model (Markov model).  The Markov model is constructed in a reduced multivariate EOF space of observed SST and sea level analysis using the methodology of Xue et al 2000.  The model is trained for the 1981-1998 period.

    The SST is the NCEP SST analysis and the sea level is from the NCEP ocean analysis.  All the data are monthly values averaged in grid boxes of 6 degrees in longitude and 2 degrees in latitude, and cover the tropical Pacific region within 19 degrees of the equator.

Forecast SST Anomaly (Degree, 3-Mon. Average) The Forecast SST Anomaly figure suggests that the sea surface temperature in the central Pacific will warm up quickly in the spring and reach about a 1 degree anomaly in the summer.

Forecast Sea Level Anomaly (cm, 3-Mon. Average) The Forecast Sea Level Anomaly figure suggests that the positive sea level anomalies in the western Pacific will move to the eastern Pacific in summer.

The full suite of Dr. Xue's model results are updated monthly and is available at: <http://www.cpc.ncep.noaa.gov/pacdir>

SPECIAL SECTION-Experimental Forecasts for Pacific Island Rainfall

     The latest results from the CPC statistical model for all predicted locations are shown below.  This map-like presentation applies only to two particular seasons (July - September 2002 and October - December 2002) of the 13 three month periods out to a year in advance that are available from the model.  The full time series in graphs and tables are updated monthly on the internet at: <http://www.cpc.ncep.noaa.gov/pacdir/CCA11.html>.

      Negative numbers are forecasts for less than normal rainfall while positive numbers are forecasts for greater than normal rainfall.  The size of the number (not the value of the number) indicates how accurate the forecast is expected to be, on the average, for the station at the given time of year and the forecast lead time.  There are three sizes: the smallest size indicates low skill, the medium size indicates moderate skill, and the largest size indicates a relatively high skill.  The value of the numbers tell how large a deviation from normal is expected.  These values are in standardized units that indicate how typical (or atypical) the rainfall conditions are expected to be relative to the station’s normal climatology.  For example, numbers from 0 to 25  (or 0 to -25) are small deviations, indicating conditions that would be considered typical of the climate for the station and the time of year.  Deviations from 25 to 60 (or -25 to -60) are moderate deviations, indicating somewhat wetter (or drier) conditions than would be expected for the station and the time of year.  Deviations of over 60 (or less than -60) are large deviations, indicating much wetter (or drier) conditions than normal for that location and time of year.

Sites Covered: (list not complete, selected sites only)
1.  Hawaii:  Hilo, Kahului, Honolulu, Lihue
2.  Guam: Anderson AFB, Guam WSFO
3.  Johnston Island
4.  Koror WSO, Palau
5.  Kwajalein Atoll
6.  Majuro WSO, Marshall Is.
7.  FSM:  Pohnpei WSO, Yap WSO, Chuuk WSO
8.  Wake Island
9.  Henderson, Solomon Islands
10.  Luganville, Vanuatu
11.  New Caledonia: Koumac, Noumea
12.  Funafuti, Tuvalu
13.  Fiji:  Rotuma, Undu Point, Nadi
14.  Hihifo, Wallis & Futuna
15.  Tonga:  Niuatoputapu, Vavau
16.  Rarotonga, Cook Islands
17.  French Polynesia:  Atnona, Bora Bora, Papeete, Takaroa, Rikitea, Tubai, Rapa


ACKNOWLEDGEMENTS AND FURTHER INFORMATION

The information contained in the LOCAL VARIABILITY SUMMARIES section and elsewhere in this
issue of the Pacific ENSO Update has been drawn from many sources.  Further information may be
obtained by contacting your local National Weather Service office, or the individuals and institutions
listed below:

NOAA National Weather Service-National Centers for Environmental Prediction (NCEP)-CLIMATE
PREDICTIONS CENTER (CPC):
World Weather Building, Washington D.C. 20233
Contact CPC at 301-763-8155 for more information on the ENSO Advisory, the Long-Lead Outlook for
the Hawaiian Islands, and other publications discussed in this bulletin.

NOAA National Weather Service-Pacific Region
WEATHER SERVICE FORECAST OFFICE (WSFO)
University of Hawaii at Manoa
HIG #225, 2525 Correa Rd.
Honolulu, HI 96822
Contact the WSFO at 808-973-5270 for more information on NWS-PR sources of climate information.

University of GUAM (UOG) WATER AND ENERGY RESEARCH INSTITUE (WERI):
Lower campus, University of Guam
UOG Station, Mangilao, Guam 96923
Contact C. Guard or M. Lander at 671-735-2685 for more information on tropical cyclones and climate
in the Pacific Islands.

University of Hawaii at Manoa
School of Ocean and Earth Science and Technology (SOEST)
Department of Meteorology
HIG #350, 2525 Correa Rd.
Honolulu, HI 96822
Contact Dr. T. Schroeder at 808-956-7476 for more information on hurricanes and climate in Hawaii.

PACIFIC EL NINO-SOUTHERN OSCILLATION (ENSO) APPLICATIONS CENTER:
University of Hawaii at Manoa
School of Ocean and Earth Science and Technology (SOEST)
Department of Meteorology
HIG #350, 2525 Correa Rd.
Honolulu, HI 96822
Contact R. Schneider at 808-956-2324 for more information on ENSO-related climate data for the Pacific Islands.
Contact C. Anderson at 808-956-3908 for more information on Pacific ENSO Update and applications.

For further information, please contact:

Rebecca Schneider
Editor, Pacific ENSO Update,
Pacific ENSO Applications Center
c/o Dept. of Meteorology, HIG Room 350
University of Hawaii - Manoa Campus
2525 Correa Road - Honolulu, HI 96822
Tel: 808-956-2324 Fax: 808-956-2877
E-mail: rsschnei@.hawaii.edu

Publication of the Pacific ENSO Update is funded in part by Grant Number NA46GP0410
from the National Oceanic and Atmospheric Administration (NOAA) Office of Global Programs.
The views expressed herein are those of the author(s) and do not necessarily reflect the views of
NOAA or any of its sub-agencies.

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