Pacific ENSO Update

2nd Quarter 2002-Vol. 8 No. 2


CURRENT CONDITIONS

    Recent climate anomalies in Micronesia and in the eastern Pacific suggest that a weak El Niño is underway.  The future strength and duration of the current weak El Niño event are not yet known, and a suite of international computer forecasts are split roughly 50-50 on the further development of El Niño in 2002.  The following ENSO advisory was posted on the U.S. Climate Prediction Center website on May 9, 2002*:
(*Please see the appendices for the June 6, 2002 ENSO Advisory)

“Warmer-than-normal sea surface and subsurface temperatures were observed throughout most of the equatorial Pacific during April 2002. Sea surface temperature anomalies were up to 2°C warmer than average in the region between the Galapagos Islands and the South American coast, and greater than 1°C warmer than average immediately to the west of 180°W. Although there was considerable warming in the eastern equatorial Pacific during February-April, which resulted in locally heavy rainfall along the coasts of Ecuador and northern Peru, there was little change in SSTs or subsurface temperature anomalies in regions farther west during this period. Consistent with this lack of evolution in the central equatorial Pacific, atmospheric indices for low-level winds, sea level pressure (SOI) and precipitation (OLR) continue to indicate near-normal conditions.
    The Madden-Julian Oscillation (MJO) is an important source of variability that can contribute to a more rapid evolution toward El Niño through related fluctuations in low-level winds and precipitation over the western and central equatorial Pacific. An eastward-propagating oceanic Kelvin wave, initiated by strong MJO activity in late 2001, resulted in the rapid warming that was observed along the coasts of Ecuador and northern Peru in early February. Since that time MJO activity has weakened and there has been no additional significant Kelvin wave activity. Without such activity a slow evolution towards El Niño conditions is possible through the remainder of 2002.
    This assessment agrees well with several coupled model and statistical forecasts, which indicate a gradual warming over the next several months with weak-to-moderate El Niño conditions by the end of 2002. It is important to add that a weak or moderate El Niño would feature considerably weaker global impacts than were experienced during the very strong 1997-98 El Niño.”

    So far in 2002, rainfall throughout Micronesia has been distributed such that the island groups to the northwest (Republic of Palau, Yap State, and the CNMI) have been a bit dry, and island groups to the east (Pohnpei State, Kosrae State, and portions of the Republic of the Marshall Islands) have been near normal or somewhat wet ( Figure 1).  A substantial portion of the first quarter 2002 rainfall in Micronesia was derived from four tropical cyclones that passed through the region during January-April 2002.  For example, of the approximately 16 inches of rain during February at WSO Chuuk, nearly 7 inches of it fell on February 28 as Tropical Storm Mitag passed near this station.

Figure 1:  Rainfall Anomaly (percent of normal) at the indicated islands for the first quarter of 2002 (January through March).

    American Samoa has had a long period of persistent dry weather.  However, 12.56 inches of rain was recorded there during March 2002, and 17.84 inches in April 2002, marking the first period in quite some time of two consecutive months with above-normal rainfall.  After the large Tropical Cyclone “Waka” passed near Samoa in December 2001, there were no further serious tropical cyclone threats to Samoa during their cyclone season.

    On the large scale, episodes of westerly winds in the equatorial latitudes of the western Pacific occurred from January 2002 through early April 2002, and were associated with four numbered tropical cyclones in Micronesia:  Tropical Storm Tapah (01W), Super Typhoon Mitag (02W), Tropical Depression 03W, and Tropical Depression 04W.  Unusually persistent episodes of westerly winds at low latitude in Micronesia and early season tropical cyclones are typical signs of El Niño, especially if the westerly winds and tropical cyclone formation persist through April and May.  During January through March, climate anomalies indicative of El Niño strengthened.  Beginning in mid-April, however, there was a return to near normal atmospheric  circulation throughout Micronesia at the same time as indicators of El Niño relaxed or failed to get stronger.  The large eastward movement of warm equatorial sub-surface ocean waters in late 2001 and early 2002 caused significant sub-surface warming in the equatorial central and eastern Pacific.  However, there has not been any significant reinforcement of the eastward movement of the western Pacific warm pool since the moderate equatorial westerly wind burst that accompanied the formation of Tropical Depression 04W during the first week of April.  Without such reinforcement, El Niño development will be slow at best and could be delayed until the following year (as has occurred with some past events).  The warm equatorial sea-surface temperatures that developed in March have recently shown some cooling to more normal values in certain areas.  While it is too early to tell if the eastward movement of the warm waters will become re-established and how intense the warming will become, it is likely that a 2002-03 El Niño event will not be nearly as strong as the 1997-98 event. The following climate anomalies are typical of an El Niño year:

(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 (especially from April onward);
(3) The formation of “early season” tropical cyclones in the Caroline Islands from March through June;
(4) An eastward expansion of the formation region of tropical cyclones into the eastern Caroline Islands and the Marshall Islands — in extreme El Niño years     like 1997 the formation region of tropical cyclones can be pushed eastward to the south of Hawaii late in the year (ie: Super Typhoon Paka);
(5) 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 generally warmer than normal.  There is a distribution of slightly warmer than normal SSTs in the western Pacific with a region of +1°C anomalous warmth on the equator near the date line.  A region of the equatorial waters near 120°W has cooled slightly and is within 0.5°C of normal.  Along the South American coast and extending westward to the Galapagos Islands, the SST is over +1°C warmer than normal with a region of +2°C anomalous warmth along the coast of Ecuador and northern Peru.

     The sub-surface ocean water temperature is generally at least 1º C warmer than normal to a depth of 150 meters in the equatorial western Pacific, eastward to the longitude of Hawaii (~155°W), and to a depth of 100 meters in the eastern equatorial Pacific to the South American coast.  Peak warm anomalies at depth occur near 165°W, where the temperature at 125 meters is over 3º C warmer than normal, and also near the South American coast where the temperature at 50 meters is over 4º C warmer than normal.  The sub-surface temperature anomalies are now greatest east of the date line and along the South American coast – an indication that El Niño has begun.

SOI

    The Southern Oscillation Index (SOI) averaged near zero for the last six months of 2001 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).  During January through March 2002, the SOI still averaged near zero:  January (+0.4), February (+0.9), and March (-0.9).  Nearly all El Niño events are associated with a persistently negative SOI.  The SOI has yet to become persistently negative which would be expected if El Niño takes hold for the remainder of 2002.
 
 

TROPICAL CYCLONE ACTIVITY

    Western North Pacific tropical cyclone (TC) activity from January through April, 2002 included 4 TCs – Tropical Storm Tapah, Super Typhoon Mitag, Tropical Depression 03W, and Tropical Depression 04W.  Each of these TCs formed in Micronesia and passed through many of the island groups.  The first tropical storm of the year, Tapah, formed in the eastern Caroline Islands and moved westward toward the Philippines.  When it passed to the south of Guam on January 8, over 6 inches of rain in 24 hours fell on parts of the island.  Tapah continued westward bringing rains to Yap State and Palau.  Late in February another TC developed in the eastern Caroline Islands.  During the first week of March, this weather system became Super Typhoon Mitag.  At the end of February, Mitag (as a tropical storm) passed over Chuuk State, bringing over  7 inches of rain in 24 hours.   Mitag intensified and passed to the south of Yap and to the north of Palau (Figure 2).  This was a damaging typhoon for Yap State.  Some damage was also sustained on Palau.

Figure 2:  Typhoon Mitag passes between Palau and Yap.  The typhoon passed much closer to Yap than Palau.  Substantial damage occurred at Yap, with some minor damage reported in parts of Palau.  Mitag intensified to a super typhoon after moving to the northwest of both these island groups.  (GMS mid-day visible image at 0400 UTC 03 April 2002.)

     Based on an expectation of a weak El Niño in 2002 (and other  climatic factors), near-normal to slightly above normal numbers of TCs in the western North Pacific is anticipated.  Two groups have issued forecasts for western North Pacific typhoons  in 2002:  The Laboratory for Atmospheric Research (LAR) at the City University of Hong Kong (http://aposf02.cityu.edu.hk/~mcg/index.htm), and The Benfield Greig Hazard Research Centre, University College London (UCL), UK (http://tropicalstormrisk.com).  The Hong Kong group forecasts 27 TCs of at least tropical storm intensity (versus a normal of 28), and 17 typhoons (versus a normal of 18).  The UCL group forecasts 31 TCs of at least tropical storm intensity and 21 typhoons.

     During El Niño the formation region of TCs expands eastward into the eastern Caroline Islands and the RMI.  This increases the risk of TCs for Guam, the CNMI, the eastern Caroline Islands, and the RMI.  TC activity gets off to an early start during an El Niño year with an increased number of TCs from March through June.  (This has already occurred with four TCs in Micronesia through April.)   During 2002, several TCs may form in Pohnpei and Kosrae States and in the RMI.  A few of these could become typhoons as they move northwestward out of the eastern FSM and may threaten Guam and the CNMI as full-fledged typhoons.



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

State of Hawaii: Two strong troughs in the middle and upper level westerlies during the first half of May produced a very wet month across the State of Hawai’i. The first event affected the island chain from 4 through 7 May. Heavy showers produced flash flooding and road closures in the Ka’u District of the Big Island on 5 May. This was followed by a period of intense thundershowers over the Ko’olau Range of O’ahu on 6 May. The resultant flash flooding along Kaukonahua Stream forced evacuations of homes near the town of Waialua and significant crop damages. Heavy rains from Kane’ohe to Kahana also forced road closures along portions of the Windward Coast. Preliminary damages to crops were estimated to be $230,000 while damages to equipment and supplies were estimated at $60,000. Fortunately there were no significant injuries or fatalities reported.

     Following 3 days of moderate trades, a second strong upper level trough dropped into the area west of Kaua’i on 11 May. As the system proceeded eastward, heavy rains from strong thunderstorms caused flash flooding on Kaua’i on 12 May and forced the closing of the Hanalei Bridge for several hours. Heavy showers continued across the island chain through 14 May though only minor flooding problems were reported.

     The period from 15 through 20 May brought the welcome return of more normal trade winds. A short wave trough passing north of the islands on 21 May triggered very intense showers over a localized portion of east Kaua’i. Radar data indicated 4 to 6 inch per hour rates and a spotter reported 6.1 inches in a 2-hour period.  Luckily, the showers were short-lived and no significant damages or injuries were noted.

    A shift in the North Pacific weather pattern pushed the surface ridge of high pressure abnormally close to the Hawaiian Islands for the remainder of the month. Land and sea breezes were the rule with no significant rainfall.

Kevin Kodama-Senior Service Hydrologist, NWSFO Honolulu, Hawaii



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

American Samoa:  Rainfall at Pago Pago Airport for January, February, and March was 7.42 inches (59%), 4.85 inches (38%), and 12.56 inches (116%), respectively, amounting to 68% of normal for the 3-month period.  After many months of mostly below normal rainfall (during 2001, only February, March, and December had above average monthly rainfall), March 2002 was slightly wetter than normal.  April 2002, with 17.84 inches (148%), was much wetter than normal.  Heavy rain events in March and April 2002 accompanied periods of an active South Pacific Convergence Zone.

     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).  Similarly, 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).  Still, on average, there is not a consistent ENSO signal in the rainfall.  There is a tendency for 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 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 Samoa for all of 2002 is for near-normal to slightly above normal rainfall.  If a very intense El Niño develops during 2002 (which is not likely), then a prolonged dry period may commence in early 2003.

     With the expected onset of at least a weak El Niño in 2002, the risk of a damaging tropical cyclone may increase for Samoa during its December 2002-March 2003 cyclone season.

Predicted rainfall for American Samoa from May 2002 through June 2003 is:
 
Inclusive Period
% of Long-Term Average
May 2002-Dec 2002
105%
Jan 2003-Jun 2003
95%
source: UOG-WERI

Guam/CNMI: Rainfall at Guam International Airport (GIA) during January, February, and March was 8.46 inches (190%), 5.55 inches (148%), and 3.05 inches (102%), respectively.  This amounted to 153% of the normal value for the period January-March.  Andersen Air Force Base (AAFB) measured 13.42 inches (235%), 6.38 inches (122%), and 4.04 inches (99%), or 159% of the average rainfall for January-March.  The first three months of 2002 were quite wet on Guam, thanks (in part) to rains associated with the passage near Guam of tropical cyclones Tapah and Mitag, and some other tropical disturbances and shear lines.  The wet conditions in January through March followed a relatively wet autumn of 2001.  After a wet January-through-March, April turned dry on Guam with only a little over an inch of rain recorded at most locations.  In April 2002, almost daily grassland wild fires (typical of Guam’s dry season) commenced.

    On Saipan, it was not nearly as wet during January, February, and March as it was on Guam.  This was partly due to the fact that some of the heavy rain events on Guam were caused by tropical cyclones and other tropical disturbances passing to the south, and these rain events did not reach Saipan’s latitude.  Rainfall at the Saipan International Airport (SIA) was 1.34 inches (42%), 2.09 inches (87%), and 1.90 inches (95%), or only 70% of the average for the period.  For the same months, Capitol Hill’s measured rainfall was much higher than at the airport with 2.23 inches (56%) in January, 5.99 inches (200%) in February, and 3.86 inches (154%) in March.  The 12.08 inches of rain at Capitol Hill during the first quarter of 2002 was the highest recorded rainfall during the quarter among all Saipan stations, and was wetter than normal at 127%.

     Rainfall amounts for January, February, and March at the Tinian Airport were 2.17 inches (69%), 3.97 inches (132%), and 1.90 inches (76%), respectively. The 3-month rainfall for Tinian Airport was below normal at 85%.  At Rota Airport, January, February, and March rain amounts were much higher than at islands to the north, and were more in line with Guam’s high totals. (Rota, located only 40 n mi north of Guam, experienced some of the same heavy rain events that occurred on Guam.)  The January, February, and March totals were 8.26 inches (156%), 6.66 inches (143%), and 3.90 inches (107%), respectively.  This gave a 3-month average of 138%.  On the northern part of Rota, at the beautiful Rota Resort and Country Club, the NASA TRMM network recorded a total of 14.67 inches of rainfall during the first quarter versus 18.82 at the airport, or 78% of the airport total.

    Based on 30 years of rainfall data, El Niño years on Guam and the CNMI average are slightly wetter than normal.  This should be expected since monsoon and tropical cyclone activity are normally greater during these years.  Guam’s wettest year on record (1976) was an El Niño year.  The extreme rainfall of that year was mostly 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 following year.  An El Niño event is anticipated to begin in 2002, however it is still too early to predict whether it will be weak, moderate or strong.  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.  An early start of tropical cyclone activity has already been noted in the western North Pacific basin.  The typhoon threat for Guam and the CNMI 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 from May 2002 through June 2003 is as follows:
 
Inclusive Period
% of Long-Term Average
---
      Guam/Rota                                              Saipan/Tinian
May 2002-Oct 2002
          120%                                                        115%
Nov 2002-Dec 2002*
           95%                                                          90%
Jan 2003-Jun 2003
           80%                                                          75%
*Unless a tropical cyclone passes near the islands.
source: UOG-WERI

Yap State:  Most of Yap State was slightly drier than normal during January, February, and March.   Much of the rain came in short durations as Tropical Storm Tapah and other tropical disturbances passed by the island.  The weather station at the Yap Airport recorded 4.77 inches (65%) in January, 6.73 inches (113%) in February, and 5.92 inches (99%) in March, or 90% of normal rainfall for the three months.  January, February, and March rainfall amounts on Ulithi were 5.26 inches (84%), 4.40 inches (87%), and 2.63 inches (52%) or 75% for the 3-month period.  Farther south at Woleai Atoll, rainfall was 3.38 inches (32%) in January, 10.48 inches (140%) in February, and 4.56 inches (55%) in March, for a 3-month average of 70%.

      In early April, Typhoon Mitag passed very close to Yap (see Figure 2) and caused substantial damage on parts of the island.  Damage to personal property was caused by coastal inundation from large waves and high winds.  The following excerpts from the Kaselehlie Press (Vol. 2, Issue No. 8, March 7, 2002. Byline: Robert Whitmore) describe the effects of Mitag:

    “Typhoon Mitag, packing winds in excess of 100 mph, smashed into Yap on Sunday, March 3.  Peak winds were felt at midday, but damages were surprisingly light.
     At Yap’s airport terminal on Sunday afternoon, sheets of metal roofing lay on the ground, and other large pieces still flapped in the receding winds on the terminal roof.  In Colonia’s harbor, a boat dragged its anchor and damaged petroleum pipelines belonging to Mobil Oil Co. [This later proved to be a major oil spill requiring clean-up efforts.]
     Most damage was minor, however.  Many local houses received some damage to their roofs, and flooding was a problem to houses and businesses located close to the water in Colonia.  On the rest of the island, most of the damage was limited to blown-down banana trees and flattened koyengs.
     Electrical power was lost on Sunday morning, but crews are working to restore power to the island.  Residents are now busy cleaning up the broken limbs and other debris blocking roads and paths.

     The following damages were reported by the Yap Weather Service Office (David Aranug, MIC):

     “The Destiny Hotel in Gilman was completely demolished.  Most of the damage was caused by storm surge.  Tidal surge advanced inland about 300 yards in some areas.
     All of the causeways in town were about 4 to 5 feet underwater during and immediately after the typhoon passed.  The broken Mobile Oil pipeline along the causeway was the result of a 30-foot boat being rammed against the pipes by heavy tidal surge.
     Some people lost their homes in Rull (part of Colonia).  The Sav-Way-Mart Store was smashed open on the back side (seaward side).  Thousands of dollars of office equipment and merchandise were washed to sea.  Stores around the lagoon lost thousands of dollars in merchandise as the stores became flooded with seawater.
     The ground floor of the ESA Hotel was also flooded.  Fortunately, there was no damage to the hotel and the guests were safe.
     Parts of the roof of the airport terminal were ripped off.  This was one of the designated storm shelter areas.  No one got hurt.”

     A day earlier, the typhoon was estimated to have passed less than 30 miles South of Woleai.  The island lost power, and reports indicated heavy damage to the breadfruit and coconut trees.  Thatched roof houses were blown down.  The observer on Woleai noted a veering of the wind from north to east to south as the typhoon passed, and estimated the wind gusts to as high as 90 knots.  Other islands affected included Satawal, Sorol, Ngulu, and Ulithi.  There was some minor damage reported from Palau State.  On May 29, 2002, President Bush declared Yap State a major disaster area, opening the way for use of federal funds to help them  recover from Typhoon Mitag.

     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.  While an El Niño event is anticipated to begin in 2002, it is too early to predict its strength.  An El Niño event in 2002 would likely produce slightly greater than average rainfall in Yap during this forecast period, with persistent dryness beginning late in the year.  Tropical cyclone activity has already had an early start in Yap State with the passage of Mitag in early March.  The tropical cyclone threat should be normal in Yap State for the second half of 2002.

Predicted rainfall for Yap State from May 2002 through June 2003 is as follows:
 
Inclusive Period
% of Long-Term Average
---
        Yap                                    Outer Atolls: 
---
        Island                     S. of 8N        N. of 8N
May 2002-Sep 2002
        105%                            110%              100%
Oct 2002-Dec 2002
          90%                              85%                90%
Jan 2003-Jun 2003
          80%                              80%                80%
source: UOG-WERI

Chuuk State:   During January, February, and March, the weather station at Weno Island measured 7.50 inches (70%), 15.93 inches (258%), and 9.75 inches (117%).  This amounted to 132% of normal totals for the 3-month period.  The very wet conditions of February were largely the result of a 24-hour rainfall of nearly 7 inches on the last day of the month as the developing Typhoon Mitag nearly passed over the island.  In the Mortlocks at Lukunoch, rainfall for January, February, and March was 5.63 inches (53%), 7.73 inches (125%), and 4.23 inches (51%), respectively.  The 3-month average was 70%.  Since it did not get the extreme rain during Mitag that Weno received, Lukunoch was much drier.  Aside from the rains associated with Mitag, many of the islands of Chuuk State were relatively dry from January through March.  Rainfall for all of Chuuk State is expected to be wetter than normal as the monsoon trough pushes into the region by May, and tropical disturbances begin to form and move through the Caroline Islands.  High month-to-month variability is possible whenever an active monsoon trough and its associated tropical disturbances produce rainfall.  Tropical cyclone activity began early in the Caroline Islands with Mitag in late February and Tropical Depression 04W in April forming in Chuuk State.  Additional tropical cyclone development is anticipated in Chuuk State during May and early June.  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 storms and typhoons.  Chuuk will have a chance of getting a tropical storm, primarily during the rest of the spring and again in October and November.

Predictions for Chuuk State from May 2002 through January 2003 are as follows:
 
Inclusive Period
% of Long-Term Average
---
    Chuuk                  Outer Atolls:
---
    Lagoon                  Southern/Western        Northern
May 2002-Sep 2002
     110%                         110%                        100%
Oct 2002-Dec 2002
      95%                            95%                          95%
Jan 2003-Jun 2003
      85%                            85%                          85%
source: UOG-WERI

Pohnpei State:   Rainfall at Pohnpei State was drier than normal on some islands and wetter than normal on others.  The highest monthly rainfall at any island in Pohnpei State during January to March 2002 was 23.23 inches recorded at Kapingamarangi during March.  A near-equatorial trough with persistent westerly winds along the equator during February and March was associated with the heavier rainfall amounts at islands located closer to the equator (such as Kapingamarangi).   At the weather station at Kolonia, the January, February, and March rainfall totals were 10.81 inches (83%), 15.13 inches (140%), and 9.66 inches (71%), respectively.  This amounted to a 3-month value of 95% of average precipitation.  At Pingelap, observed rainfall in January, February, and March was 10.34 inches (84%), 11.33 inches (93%), and 11.55 inches (80%), respectively, for a 3-month amount of 85%.  At Nukuoro, January through March precipitation amounts were 12.17 inches (104%), 15.54 inches (147%), and 19.94 inches (147%), respectively, for a 3-month amount of 133%.  Kapingamarangi was actually drier than normal during January and February, but picked up a substantial amount of rain during March as convection in persistent equatorial westerly wind flow produced abundant rains.  January, February, and March rainfall measurements there were 8.26 inches (79%), 9.26 inches (90%), and 23.23 inches (167%), respectively.  Kapingamarangi has had abundant rainfall since April 2001; the 9-month average from April though December 2001 was 160% of normal.  Convection along the equator and enhanced monsoonal westerlies have kept Kapingamarangi in rainfall surpluses for almost every month since April 2001.

     Rainfall for all of Pohnpei State is expected to be wetter than normal as the monsoon trough moves into the Caroline Islands in May.  High month-to-month variability is possible whenever rainfall is produced by an active monsoon.  Tropical cyclone activity has already had an early start in Pohnpei State with the formation in late February of Typhoon Mitag, and Tropical Depression 04W in early April.  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 storms or typhoons.  Pohnpei will have a chance of getting a tropical storm, primarily during the rest of the spring and again in October through December.

    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 appears to be underway in 2002, however it is still too early to predict whether it will be weak, moderate or strong.  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.

Predicted rainfall for Pohnpei State from May 2002 through June 2003 is as follows:
 
Inclusive Period
% of Long-Term Average
---
     Pohnpei                           Outer Atolls:
---
      Island                 Eastern     Southern     Equatorial
May 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 (SAWRS) during January, February, and March was 20.59 inches (143%), 16.26 (99%), and 25.93 inches (139%), respectively.  The 3-month total of 62.78 inches was 127% wetter than the normal total of 49.41 inches.  Much of the abundant rainfall in the first quarter of 2002 occurred in association with several tropical disturbances and other mesoscale convective features at the eastern end of the near-equatorial trough.  The tropical disturbances that became Tropical Storm Tapah and Super Typhoon Mitag produced substantial rainfall in Kosrae State.  The January to March totals at Kosrae (SAWRS), Utwe, Tafunsak, and Tofol were 62.78 inches (127%), 48.01 inches (97%), 55.69 inches (113%), and 66.90 inches (135%), respectively.

    Rainfall for Kosrae is expected to be above normal from May 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.  In keeping with El Niño onset in 2002, some tropical disturbances that later became tropical cyclones have already formed near Kosrae:  (1) the tropical disturbance that became Tropical Storm Tapah in January, (2) the tropical disturbance that became Super Typhoon Mitag in late February, and (3) the tropical disturbance that became Tropical Depression 04W in early April.  There is a slight risk that Kosrae could experience one or two periods of rough seas, gusty winds, and heavy rains from developing tropical cyclones forming near or to the west of Kosrae State for the remainder of the spring, and then again during October through December 2002.  Dry conditions associated with El Niño may begin in late 2002.

Predicted rainfall for Kosrae State from May 2002 through June 2003 is as follows:
 
Inclusive Period
% of Long-Term Average
May 2002-Sep 2002
110%
Oct 2002-Dec 2002
95%
Jan 2003-Jun 2003
85%
source: UOG-WERI

Republic of Palau:  Rainfall at Koror during January, February, and March was 12.57 inches (117%), 4.50 inches (49%), and 9.60 inches (117%), respectively.  The 3-month average was 95% of normal.  For the 3-months of January, February and March, the monthly rainfall distribution at Nekken Forestry was slightly drier than at the airport with 6.67 inches, 4.26 inches, and 8.59 inches respectively.  Farther south at Peleliu, conditions were also drier with 8.13 inches in January, 4.62 inches in February, and 8.20 inches in March.  The first quarter 2002 total at Nekken Forestry was 19.52 inches (70% of normal), and at Peleliu it was 21.43 inches (76% of normal) – each a bit drier than at Koror where the first quarter total was 26.67 inches (95%).

     The weak El Niño event now in progress may strengthen during the remainder of 2002, however, it is still too early to predict whether it will remain a weak event, or become moderate or strong.  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.  In keeping with El Niño onset in 2002, some tropical cyclones have already formed in Micronesia and passed near Palau:  (1) Tropical Storm Tapah in January,  (2) Super Typhoon Mitag in early March (which caused some minor property damage in parts of Palau), and (3) Tropical Depression 03W in mid-March.  Yet another tropical storm could affect Palau in May or June.  With higher tropical cyclone activity expected eastward near the date line in the late season, the tropical cyclone threat for Palau will likely be near normal from now until September, and then below normal from September through December.

Predicted rainfall for Palau from May 2002 through June 2003 is:
 
Inclusive Period
% of Long-Term Average
---
       Koror and                     Outer Atolls:
---
      Mountain Is               N. of 8N    S. of 8N
May 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):    Abundant rainfall in the first quarter of 2002 occurred in association with several tropical disturbances and other mesoscale convective features at the eastern end of the near-equatorial trough.  The Majuro weather station (representative of the southern islands) measured 9.00 inches (107%), 6.80 inches (110%), and 7.57 inches (91%) during January, February, and March, respectively.  For the 3-month period, the average for Majuro was a near-normal 102%.  Rainfall at Kwajalein (and nearby Ebeye) was only 1.31 inches (29%) in January, 3.24 inches (100%) in February, and 5.50 inches (134%) in March, for a 3-month average of 85%.  Kwajalein (representative of the central islands) was dry for 10 of 12 months in 2001 (only October and November were wetter than normal).

     Farther north, Wotje continued to be the driest of the locations in the RMI that measured rainfall, with 1.16 inches in January, 2.78 inches in February, and 2.14 inches in March. 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 anticipated to slowly strengthen for the remainder of 2002, although it is too early to predict whether it will become a moderate or strong event, or remain weak.  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 strong El Niño events.  After weak El Niño events, the rainfall at Kwajalein and the northern islands of the RMI tends to be below normal, but at Majuro, it remains near normal.  The line of zero correlation of rainfall with El Niño runs through the southern Marshall Islands, and the effect of El Niño reverses near the equator.  (For example: at Tarawa, where El Niño years are wet, and La Niña years are dry.)  So far in 2002, there has been an early start of tropical cyclone activity in the western North Pacific, with development of tropical disturbances in the RMI, some that later moved west and became tropical cyclones.  The tropical cyclone threat for the RMI should be slightly elevated for the remainder of the year, with October through December being the months of greatest threats when the monsoon trough should extend eastward into the RMI.

Predicted rainfall for the RMI from May 2002 through June is as follows:
 
Inclusive Period
% of Long-Term Average
---
           Southern     Central      Northern 
---
             Islands       Islands       Islands
May 2002-Sep 2002
              105%         105%         100%
Oct 2002-Dec 2002
              100%          100%          90%
Jan 2003-Jun 2003
               95%           100%          80%
source: UOG-WERI



APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 13 June 2002, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY:  issued by Climate Prediction Center/NCEP on June 6, 2002

    Further evolution toward a Pacific basin-wide warm episode (El Niño) was observed during May 2002, as sea surface temperature (SST) anomalies increased throughout the equatorial Pacific between 170°E and 95°W. By the end of May warmer-than-normal SSTs were observed over a large portion of the equatorial Pacific, with departures from average greater than +1°C in the region from 165°E to 135°W and also locally between 130°W and the South American coast. This warming represents a significant transition from the localized warmth (central equatorial Pacific and South American coast) earlier this year, observed during recent months, toward a more extensive basin-wide warming typical of El Niño/Southern Oscillation (ENSO) events.

     This warming resulted from a significant weakening of the equatorial easterly wind throughout the Pacific related to the Madden-Julian Oscillation (MJO). The MJO is an important source of variability that can contribute to the evolution toward El Niño through related fluctuations in low-level winds and precipitation over the western and central equatorial Pacific. An eastward-propagating oceanic Kelvin wave, initiated by strong MJO activity in late 2001, resulted in the rapid warming that was observed along the coasts of Ecuador and northern Peru in early February. Subsequently, MJO activity was relatively weak during early 2002, with no additional significant Kelvin wave activity during that period. However, in late April 2002 the MJO intensified and during the last half of May the low-level equatorial easterly winds substantially weakened throughout the Pacific, accompanied by an increase in equatorial SST anomalies. NOAA TAO buoy data indicate that the oceanic thermocline has deepened east of the date line (180°W) since mid-May, consistent with the basin-wide weakening of the low-level equatorial easterly winds. This deepening may be an indication of renewed Kelvin wave activity.

     Given the recent strength of the MJO and its period of about 40 days, it is likely that significant month-to-month fluctuations will continue to occur in many atmospheric indices used to monitor the ENSO cycle. In spite of this variability, the overall trends in SSTs and some atmospheric indices (Southern Oscillation Index, 850-hPa zonal wind) in recent months indicate that further development of El Niño will continue. Consistent with this assessment, most statistical and coupled model forecasts indicate that weak-to-moderate El Niño conditions will continue through the end of 2002.

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 warm anomalies in the central-western Pacific will grow and spread to the eastern Pacific in the fall, and reach 1.2 degree amplitude in the winter of 2002/2003.

Forecast Sea Level Anomaly (cm, 3-Mon. Average)
The Forecast Sea Level Anomaly figure suggests that the positive sea level anomalies in the south-western Pacific will move to the equatorial eastern Pacific, and the negative sea level anomalies in the north-western Pacific will grow substantially in the fall and winter.

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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