Pacific ENSO Update

4th Quarter 2003-Vol. 9 No. 4


CURRENT CONDITIONS

   
       Recent patterns of the atmospheric circulation and the oceanic sea surface temperature distribution in Micronesia and in the central Pacific indicate that the climate of the region remains in a phase that is neither El Niño nor La Niña: a condition recognized as El Niño Neutral.  The widespread dryness that was expected to occur in Micronesia through the first six months of 2003 did not materialize, and most locations received adequate rainfall. Throughout all of Micronesia, rainfall during the first half of 2003 was much greater than in most such periods during years that follow El Niño.  Rainfall during July through November has generally been near normal in most locations (Figure 1a, b), with some large monthly values and large month-to-month variations in certain places.

   During the first half of 2003, four tropical cyclones (Tropical Storm Yanyan, Super Typhoon Kujira, Typhoon Chan-Hom, and Typhoon Soudelor) affected parts of Micronesia in January, April, May, and June respectively.  Beginning in July 2003, tropical cyclone formation shifted farther to the west, and areas affected by typhoons included the Philippines, Japan, and China.  Many of the precursor tropical disturbances to these tropical cyclones produced some periods of heavy rainfall in Chuuk State, Yap State, Palau, Guam, and the CNMI.  With respect to the behavior of tropical cyclone formation, the atmosphere is now exhibiting behavior typical of years after an El Niño (i.e., nearly all tropical cyclones have formed west of the longitude of Guam (145°E)).  Thus, most of Micronesia enjoyed a welcome break from the numerous tropical storms and typhoons that plagued the region during 2002.  This bit of good fortune was shattered in November 2003, when Typhoon Lupit severely affected some of the islands and atolls of Chuuk State and Yap State.

    A suite of international computer forecasts of El Niño are in general consensus that the climate will remain El Niño Neutral (a climate state that is neither El Niño nor its opposite, La Niña) for the next six to nine months.  ENSO neutral conditions do not preclude the occurrence of localized extreme weather events such as typhoons, flash floods, extreme dryness at some islands, or other types of dangerous environmental conditions such as hazardous surf.  It is, however, often easier during El Niño or La Niña to identify and predict the occurrence of large-scale changes to rainfall patterns and tropical cyclone tracks.  Recent computer forecasts are hinting at a possible return to weak El Niño conditions sometime in 2004.  The following ENSO Forecast Forum was posted on the U.S. Climate Prediction Center web site on November 06, 2003:

   “Equatorial surface and subsurface temperatures were warmer than average throughout most of the Pacific during October.  SST anomalies greater than +0.5°C (~1°F) were observed in most areas along the equator between Indonesia and the South American coast. By the end of the month, positive SST anomalies were observed in all of the Niño regions.  However, the 850-hPa zonal wind indices (central and western equatorial Pacific values near zero), OLR index (near zero), 200-hPa zonal wind index (near zero), SOI and EQSOI (near zero) all indicate ENSO-neutral conditions. These indices do not show any significant trends that would support either additional large-scale increases or decreases of SST anomalies in the equatorial Pacific.

   A majority of the statistical and coupled model forecasts indicate near neutral conditions (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) for the remainder of 2003 and early 2004. However, over the past few months there has been a trend in the suite of forecasts towards somewhat warmer conditions, consistent with observed trends in SST anomalies. If the observed Niño 3.4 SST anomaly for October 2003 (+0.6°C) persists through November, the three-month (September-November) running mean value of this index would reach the NOAA threshold (+0.5°C) for El Niño. Thus, it is likely that borderline El Niño/ENSO-neutral conditions will persist in the equatorial Pacific through the Northern Hemisphere winter of 2003-04. Further evolution of warm-episode conditions is possible if persistent enhanced equatorial convection (cloudiness and rainfall) develops in the vicinity of the date line (180°W), accompanied by weaker-than-average equatorial low-level easterly winds over the central and western Pacific.”

 

SST

   El Niño conditions ended in the spring of 2003 as the sea surface temperature (SST) anomalies decreased across the equatorial Pacific to below the threshold values for El Niño.  The cooling of the SSTs did not progress to the colder-than-normal values necessary for La Niña, but generally remained slightly above normal in the central equatorial Pacific, and slightly colder than normal along the coast of South America.  Since September of 2003, the SST across the central and eastern equatorial Pacific has warmed somewhat to values just below the borderline of a weak El Niño.  Despite this slight warming trend in the equatorial Pacific, all atmospheric behavior remains typical of El Niño Neutral conditions, and the typhoon distribution of 2003 has been typical for a year following an El Niño.

   For the past several months, ocean temperatures at thermocline depth (50-100 m) have remained 1-2°C above normal in the central equatorial Pacific and 1-2°C below normal in the far eastern Pacific near the coast of South America.  The temperature of the subsurface ocean water is now substantially cooler since its peak warmth in December 2002. 

SEA LEVEL

   During El Niño, the sea level falls throughout most of Micronesia.  During most El Niño events the sea level fall is approximately 0.5 meter below the La Niña high stands of the sea.  The sea level typically drops to its lowest magnitude at the end of the El Niño year, and then quickly rises to above normal by May or June of the following year.  During the years 1999, 2000, and 2001, the sea level was well above normal in Micronesia.  By December 2002, the sea level throughout most of Micronesia fell to its minimum value.  In some places this was over 40 cm lower than its 1999 high point.  The greatest lowering of the sea level (20 cm below normal) was observed in the region of Palau and Yap.  The sea level fell to nearly 10 cm below normal all the way east to the northern Marshall Islands.  By February 2003, the sea level had recovered to near normal levels throughout much of Micronesia.  By June 2003, the sea level was once again above its long-term average.  The sea level throughout Micronesia should remain near normal to slightly above normal through 2004.

SOI
   The Southern Oscillation Index (SOI) was near -1.0 from May 2002 to June 2003.  During July 2003 the SOI rose to +0.2, the first time that the SOI was positive since February 2002.  Since July, 2003, the value of the SOI has been slightly below zero each month from August to October 2003 (-0.3, -0.1, and -0.3 respectively).  This is typical behavior for the SOI during El Niño Neutral conditions.  Nearly all El Niño events are associated with a persistently negative SOI hovering near -1.0 or lower.  When an El Niño event ends, the SOI usually rises to near zero or becomes positive.  During La Niña, the SOI is persistently positive, hovering near +1.0 or higher.  Consistent with the continuation of El Niño Neutral conditions, the SOI should remain near zero for the next six to nine months.
 

TROPICAL CYCLONE ACTIVITY

  Through November of 2003, there were 26 tropical cyclones in the western North Pacific that were numbered by the Joint Typhoon Warning Center (JTWC) in Hawaii.  The Japan Meteorology Agency (JMA) named 21 of them.  Tropical cyclones that have affected Micronesia include: Tropical Storm Yanyan (01W) that formed near Pohnpei in mid-January and traveled toward Guam; Super Typhoon Kujira (02W) that formed near Pohnpei and tracked to the south of Guam;  Typhoon Chan-hom (04W) that formed in Chuuk State causing gales and heavy rain; Typhoon Krovanh (12W) that passed almost directly over Guam on August 19 as a tropical depression; Typhoon Dujuan (14W) that formed north of Guam and Saipan in late August and later affected Hong Kong in early September; Typhoon Maemi (15W) that formed near Guam and later became one of the most intense typhoons to strike the Korean Peninsula; Typhoon Koppu (16W) that formed north of Guam and Yap as a large monsoon depression; Typhoons Ketsana (20W) and Parma (21W) that formed north and west of Guam and helped to establish the first prolonged episode of southwesterly winds for Guam and the CNMI in 2003 during mid-October; Typhoon Melor (24W) that passed across most of Micronesia from Pohnpei to Palau as a weak tropical disturbance before becoming a typhoon just east of Luzon; Typhoon Nepartak (25W) that formed near Chuuk and passed between Guam and Yap in early November as a tropical depression; and Typhoon Lupit (26W) that formed north of Kosrae and became a typhoon when in Chuuk State.  Typhoon Lupit was a major typhoon for Micronesia and caused substantial damage to crops and vegetation in Chuuk State and Yap State.   The total (so far) of 26 numbered tropical cyclones in the western North Pacific through November of 2003 is five short of the normal of 31 for the year.  Unless December can produce five or more numbered tropical cyclones in the Western North Pacific, the total number of tropical cyclones for 2003 will fall below normal, which is typical for the year following an El Niño.  A below normal number of tropical cyclones in the western North Pacific during 2003 will verify the annual forecast of tropical cyclone activity made by the Laboratory for Atmospheric Research (LAR) at City University of Hong Kong (Professor Johnny C.L. Chan, Chair and Dean).  This forecast called for two less than normal tropical cyclones reaching at least tropical storm intensity, and one typhoon less than normal.



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:  November is normally the most active month for heavy rain and flash flood events in Hawaii and November 2003 certainly lived up to this expectation. During the Thanksgiving weekend, a shear line passing beneath an upper level trough dropped heavy rains over east Maui (28 November) and windward Oahu (29 November). The east Maui event produced 24-hour totals of 9.20 inches at West Wailuaiki and 4.65 inches at Oheo Gulch. No significant injuries or damages were reported as a result of these rains. Heavy rains subsequently impacted the windward slopes of the Koolau Range on Oahu, dropping 11.47 inches at Wilson Tunnel, 10.36 inches at Luluku, and 8.61 inches at Waihee Pump. Waikane Stream briefly overflowed its banks and forced the closure of Kamehameha Highway. Several homes also reported flood damages. Fortunately, no significant injuries were caused by the rains and flooding.

   Mainly moderate trade winds occupied the period from 1 through 9 November. This was followed by fresh to strong trade winds from 10 through 20 November with trade wind strength peaking on 19 November. Recurring showers embedded within the strong trades brought abundant rainfall to the east-facing slopes of the island chain but no significant flooding problems.

   A kona low northeast of the Hawaiian Islands followed by an area of low pressure north of the state brought shifting winds to the island chain from 21 through 26 November. Cool northerly winds from 21 through 23 November were followed by moist southwesterlies on 25 November and west winds on 26 November. Shower lines embedded within the southwest flow brought the most rain during this period, but totals remained below an inch.

Kevin Kodama
-Senior Service Hydrologist, NWSFO Honolulu, Hawaii



For a more complete summary, and the county by county wrap-ups, please see the November 2003 Precipitation Summary from the National Weather Service Honolulu Weather Forecast Office.

American Samoa:  Rainfall at Pago Pago Airport for July, August, and September was 12.43 inches (198%), 6.71 inches (101%), and 4.32 inches (65%), respectively, amounting to 120% of normal for the 3-month period (Figure 1b).  To date, the rainfall in American Samoa has averaged near normal for 2003.  An isolated extreme event occurred on May 19th, 2003 when torrential rains produced flash floods in streams, slope failures, and excessive ponding of water.  Four deaths were reported as well as numerous injuries and extensive damage to roads, homes, and bridges.

   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 at American Samoa have occurred in association with major El Niño events, and some prolonged very wet periods have occurred in years prior to major El Niño events.  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.  Although the period December 2002 through April 2003 was persistently drier than normal, abundant rains returned in May.  The dry season months of June through October have averaged slightly wetter than average.

   The threat of a tropical cyclone adversely affecting American Samoa will be near normal from January through March 2004.

    Computer forecasts indicate that the upcoming rainy season in American Samoa (November 2003 through April 2004) may be slightly wetter than normal overall, followed thereafter by drier than normal conditions for the remainder of 2004.  Long-range computer rainfall forecasts, however, have only limited skill in the tropical Pacific islands. 

   Predicted rainfall for American Samoa from December 2003 through December 2004 is: 
 
Inclusive Period
% of Long-Term Average
Dec 2003 - April 2004 (Rainy Season)
110%
       May - Sep 2004 (Dry Season)
                             85%
Oct - Dec 2004 (Rainy Season Onset)
95%
source: UOG-WERI

Guam/CNMI:  Rainfall on Guam during 2003 has seen very large month-to-month shifts.  An unexpectedly wet 2003 dry season (January through June) on Guam gave way to a relatively dry beginning to the 2003 rainy season in July and August.  Then, during September through November, it was exceptionally wet.  During November 2003, monthly rainfall totals set all-time records, and the total for November was greater than that of July and August combined.   The 20.33 inches of rain during November 2003 was the wettest November in 50 years of record keeping at the Guam International Airport (GIA), easily topping the previous record total of 16.15 inches in November 1978.

   Rainfall at GIA during July, August, and September was 10.16 inches (86%), 9.53 inches (65%), and 21.74 inches (147%), respectively, amounting to 100% of normal for the 3-month period.  The October total was 12.65 inches (108%) and the November total was a record 20.33 inches (239%).  There was high spatial variation and high month-to-month variability of rainfall totals across Guam throughout the first nine months of 2003, reflecting the small-scale convective nature of the rainfall events.  Surface winds were light for much of the period May through August 2003 with no occurrences of strong southwesterly monsoon winds.  Thus, the dominant rainfall regime was scattered daily island thunderstorms.  During September, several tropical disturbances (that later became numbered or named tropical cyclones) passed near Guam, and brought brief periods of heavy rain.  During October, the first prolonged (several days) episode of southwesterly monsoon winds occurred.  This was accompanied by 6-8 inches of rain, which was approximately half the monthly total.  Strong and gusty southwest winds associated with this monsoon episode resulted in the death of a woman when a cement block anchoring the tie-down of a canvas tent at an outdoor shopping arcade flew into the air (connected to its tether) and struck the woman on the head.  In mid-November, an unusually persistent line of thunderstorms produced heavy rain and over 12 continuous hours of lightning activity over Guam.  Heavy rains during the passage of Typhoon Lupit south of the island near the end of the month contributed over six inches of rain toward a record 20.33 inches monthly total at the GIA.  

   Andersen Air Force Base (AAFB) measured 10.60 inches (97%), 10.97 inches (82%), and 17.62 inches (131%), or 104% of the average rainfall for July through September.  The rain gage network at the University of Guam (UOG) was once again one of the driest places on the island.  There were 10.04 inches (95%), 7.33 inches (53%), and 19.84 inches (99%) during the months of July, August, and September, respectively.  

   The expected post-El Niño drought failed to materialize in the CNMI during January through June.  However, persistent dryness occurred on Saipan during the third quarter.  Guam’s heavy September rainfall (largely a result of a few days with high totals from thunderstorms) was not experienced on Saipan, although it was reflected in higher rainfall totals at other islands of the CNMI.  Rainfall at the Saipan International Airport (SIA) for July, August, and September was 5.02 inches (62%), 6.84 inches (55%), and 7.58 inches (56%), or only 57% of the average for the quarter (which is the heart of Saipan’s rainy season).  Rainfall recovered on Saipan in October with a monthly total of 14.50 inches (the wettest month of 2003 – so far – on Saipan).  As on Guam during the first half of 2003, there was wide variation in the rainfall from place to place.  For example, Capitol Hill’s measured rainfall was higher than the amount recorded at the airport with 6.78 inches (75%) in July, 9.58 inches (77%) in August, and 12.26 inches (91%) in September.

   Rainfall amounts for July, August, and September at the Tinian Airport were 5.47 inches (61%), 9.68 inches (77%), and 15.21 inches (113%), respectively.  The 3-month rainfall at the Tinian Airport for the third quarter of 2003 was below normal at 87%.  At Rota Airport, July, August, and September rain amounts were 6.72 inches (64%), 4.38 inches (33%), and 19.17 inches (143%), respectively.  This gave a 3-month average of 82%.  The western half of Rota has recovered well from the effects of the wind blasting brought by Typhoon Pongsona in December 2002.  

   The very dry conditions that follow an El Niño year tend to start in November and carry four to seven months into the following year.  With an El Niño event in 2002, it was expected that Guam and the CNMI would have a substantial reduction of rainfall from November 2002 through June 2003.  This did not occur.  Several tropical disturbances, some tropical cyclones, and shear lines provided adequate rainfall during this period.  Later, during July and August, surface winds were predominantly from the east with no episodes of strong monsoonal southwesterly winds.  This has been associated with much drier conditions in July and August of 2003 than during July and August 2002 when monsoonal winds were persistent and several tropical cyclones affected the islands.  It was noted in the last ENSO Update that unless there were some episodes of strong monsoonal southwesterly winds and accompanying heavy rainfall, or passages near the island of tropical cyclones, it was likely that the rainfall for the remainder of 2003 (September through December) would fall somewhat below normal.  The first (and only) episode of strong southwesterly monsoonal wind occurred on Guam and in the CNMI in mid-October, accompanied by several days of heavy rainfall.  Several tropical cyclones in their stages as tropical disturbances began to affect Guam and the CNMI almost weekly during September through November, with one full-fledged typhoon passing to the south of Guam in late November.  The monsoon episode of October, the several incipient tropical cyclones, and the passage south of the islands of Typhoon Lupit helped to produce abundant monthly rainfall totals at most islands for September, October and November.  The threat of a late-season typhoon for Guam and the CNMI should be normal for December 2003 and January 2004.  This means that approximately one or two tropical cyclones should brush past Guam and Saipan within 300 miles, but that a direct hit by a typhoon is unlikely.

   Predicted rainfall for the Mariana Islands from December 2003 through December 2004 is as follows:

Inclusive Period
% of Long-Term Average
---
      Guam/Rota                                              Saipan/Tinian
    Dec 2003 - May 2004 (Dry Season)
           100%                                                         95%
Jun - Jul 2004 (Rainy Season Onset)
            95%                                                          90%
 Aug - Dec 2004 (Heart of Rainy Season)
           100%                                                         95%
source: UOG-WERI

Yap State:  Stations on the main island of Yap and on the atolls of Yap State all experienced persistent dryness from November 2002 through February 2003, then many stations were much wetter than normal during the second and third quarter months of April through September.  The Weather Service Office near the Yap Airport recorded 24.42 inches (168%) in July, 13.51 inches (89%) in August, and 17.40 inches (129%) in September, or 128% of normal rainfall for the three months.  Rainfall amounts on Ulithi were 4.41 inches (36%) in July, 7.56 inches (59%) in August, and 22.82 inches (199%) in September, or 95% for the 3-month period.  Farther south at Woleai Atoll (which is normally wetter than Yap and Ulithi year-round), persistent dryness occurred throughout most of October 2002 through May 2003.  However, beginning in July abundant rainfall returned to Woleai.  The rainfall there was 15.33 inches (110%) in July, 15.22 inches (104%) in August, and 11.97 inches (102%) in September, for a 3-month average of 105%.

    Early in the morning of 25 November, Typhoon Lupit passed close to the Islands of Fais and Ulithi in Yap State (Figure 2).  A day earlier the typhoon passed to the north of Woleai.   Although it spared these islands a direct hit, the closeness of the passage (within approximately 60 miles to the northeast of Ulithi, within approximately 40 miles to the northeast of Fais, and within approximately 40 miles to the north of Woleai) caused some major problems.  Wind gusts to 100 mph were recorded at Ulithi.  No wind recordings were available from Fais (the island that was closest to the typhoon center).  Much of the damage was attributed to inundation from high waves that completely washed across some of the islands of the atolls.  Airport runways on Woleai and on Ulithi were covered by sea water, rocks and other debris.  Planted crops such as taro were lost to sea inundation, and coconut and breadfruit trees were severely damaged by high winds.  The main island of Yap was largely spared the damaging effects of this typhoon, however winds gusted to 60 mph at the Yap Airport.  As well, high winds and waves resulted in inundation of some low-lying residences.  Fortunately, there were no deaths or serious injuries attributed to this typhoon in Yap State.  The effects of Typhoon Lupit may be long-lasting.  Many of the islands of Ulithi Atoll face a complete loss of crops and salt-saturated soil that will take at least a year before it can grow crops again.

    In the last ENSO Update it was noted that the tropical cyclone threat at Yap would be slightly higher than normal through the rest of 2003.  The focus of tropical cyclone activity in the western North Pacific seems to have shifted west from where it was in 2002 when Guam, Chuuk, and Pohnpei took the brunt of several tropical cyclones (although Yap State was struck hard by Typhoon Mitag in March of 2002).  It is typical for tropical cyclones to form west of normal during years that follow El Niño.  Although Lupit became a tropical storm when it was between Chuuk and Pohnpei, it waited until entering Yap State to become a typhoon.  After passing Yap, Lupit moved to the northwest and became one of the most intense typhoons of 2003 (fortunately while over open ocean, away from any islands).

   Predicted rainfall for Yap State from December 2003 through December 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Dec 2003 - June 2004 (Dry Season)
  90% 
July - Oct 2004 (Rainy Season)
  100%
Nov - Dec 2004
   95% 
source: UOG-WERI

Chuuk State:  Rainfall at islands and atolls throughout most of Chuuk State has been abundant for most of 2003.  During July, August, and September, the Weather Service Office at Weno Island measured 21.65 inches (179%), 12.13 inches (83%), and 23.73 inches (206%).  This amounted to 151% of normal rainfall for the 3-month period.  The three month total of 57.51 inches was the second highest total recorded at any station in Micronesia during the third quarter of 2003
(Figure 1b).  At Lukunoch, rainfall for July, August, and September was 16.63 inches (137%), 11.42 inches (78%), and 14.14 inches (123%) for the respective months.  This amounted to 110% of normal for the 3-month period.  At Polowat in the western atolls, the rainfall was drier overall than in other parts of Chuuk with totals for July, August, and September of 18.90 inches (126%), 6.29 inches (42%), and 6.85 inches (52%), or 74% of normal for the 3-month period.  

   Three tropical cyclones affected Chuuk State in the first half of 2003:  the tropical disturbance that became Tropical Storm Yanyan in January, Typhoon Kujira in April, and Typhoon Chan-Hom in May.  Typhoon Krovanh (12W) formed just north of the main islands of Chuuk in mid-August, but had no serious effects.  Then, during the latter half of November 2003, Super Typhoon Lupit (while still a tropical storm) passed through Chuuk State and caused severe damage to crops in the northern atolls (the Hall Islands and Namonuito).  Nearly all crops (taro, breadfruit, and coconuts) were damaged by high winds and sea inundation from high waves at islands in these atolls of Chuuk State.  Several houses were destroyed.  Fortunately Lupit was only a tropical storm in Chuuk State, and intensified to minimal typhoon status as it passed from the western Chuuk Islands of Namonuito into the eastern part of Yap State.  There were no reports of deaths or serious injuries.

   The threat from a late-season tropical cyclone for Chuuk State for the rest of December 2003 and January 2004 should be near normal.  

   Predicted rainfall for Chuuk State from December 2003 through December 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Dec 2003 - May 2004
  105% 
June - Sep 2004
  100%
Oct - Dec 2004
   95% 
source: UOG-WERI

Pohnpei State:  During the first half of 2003, rainfall at Pohnpei State was heavier and more frequent than expected.  Anticipated moderate drought conditions did not materialize after the 2002 El Niño.  Rainfall during April 2003 was extremely heavy in part due to the close passage of Typhoon Kujira when it was still a tropical storm.  During July, August, and September, conditions on Pohnpei became drier.  Winds were light, only a few tropical disturbances passed through the region, and rainfall was strongly diurnal with daytime thunderstorms over the central part of the island that decayed by late afternoon.  At the Weather Service Office at Kolonia, the July, August, and September rainfall totals were 15.17 inches (82%), 11.36 inches (69%), and 12.48 inches (78%), respectively.  This amounted to a 3-month total of 39.01 inches or 77% of average precipitation.  At Pingelap, observed rainfall in July, August, and September was 17.52 inches (110%), 8.84 inches (59%), and 13.45 inches (90%), respectively, for a 3-month amount of 87%.  At Nukuoro, July through September precipitation amounts were 15.95 inches (111%), 12.67 inches (112%), and 8.21 inches (75%), respectively, for a 3-month amount of 100%.  Rainfall at Kapingamarangi continued to be abundant, even as its relatively modest dry season began.  During July through September the observed rainfall at Kapingamarangi was 13.65 inches (131%), 8.09 inches (131%), and 13.07 inches (221%) respectively, for a 3-month amount of 155%.  This was the highest percent of normal rainfall at any island in Micronesia during the third quarter of 2003  (Figure 1b).  

   Tropical cyclones and several tropical disturbances that later became named tropical cyclones affected Pohnpei State through most of 2002 and again during the first half of 2003.  Since Kujira’s passage near Pohnpei in April, however, most of the tropical cyclone activity in the western North Pacific has shifted west and has not affected the eastern Carolines or the Marshall Islands. 

     In cooperation with the Conservation Society of Pohnpei (CSP), and with help from the Nature Conservancy and the local office of the National Weather Service, researchers from the University of Guam have set up a network of electronic and manual rain gages all over Pohnpei from coastal locations to the highest mountain peak in the center of the island.  These rain gages (supported by a grant to the UOG from the United States Geological Survey) are intended to supply information about the distribution of rainfall on the island to help water resource managers and other groups effectively care for Pohnpei’s unique rain forest, water resources, and agriculture.  The network was activated on June 6, 2003, and data has been successfully collected since then.  The last data collection was obtained by personnel from the CSP on November 17th.  This data included a rainfall event on October 29th that caused some local flooding and isolated landslides.  The rainfall on that day was the heaviest daily total observed by the network so far: 6.60 inches of rain fell at the College of Micronesia, 4.38 inches fell at the airport, and 5.61 inches fell on the top of the highest mountain, Nahna Laud.  At the College of Micronesia, 3.95 inches fell in one hour between 5 and 6 pm local time.  

   Predicted rainfall for Pohnpei State from December 2003 through December 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
--- 
Pohnpei Islands and Atolls            Kapingamarangi
Dec 2003 - Feb 2004
             95%                                     105%
Mar - Sep 2004
            100%                                    100%
Oct 2004 - Dec 2004
             95%                                      85%
source: UOG-WERI

Kosrae State:  Kosrae was slightly drier than normal during the first half of 2003, but rainfall increased to near normal in the third quarter.  Rainfall at Kosrae (SAWRS) during July, August, and September was 13.79 inches (81%), 16.89 (102%), and 16.47 inches (96%) respectively.  The 3-month third quarter total of 47.15 inches was 93% of the normal total of 50.70 inches.  Tafunsak, and Utwa had third-quarter sums of 47.09 inches (93%) and 38.87 inches (77%), respectively.  The modest rainfall deficit on Kosrae during the first half of 2003 has had no significant impact on water resources or vegetation.  On or about November 19, 2003, the tropical disturbance that much later became Super Typhoon Lupit passed north of Kosrae.  This tropical disturbance produced some heavy rainfall in Kosrae.  The Director of the UOG Water and Environmental Research Institute, Dr. Leroy Heitz, was in Kosrae at this time, and was hiking with friends when an exceptionally heavy downpour occurred.  This led to a spectacular run-off that produced white cascading waterfalls over the steep cliff faces of the interior mountains.

   Rainfall for Kosrae State is expected to be near normal for the next 9 to 12 months.  The threat posed by tropical cyclones to Kosrae will be near normal during 2004.

   Predicted rainfall for Kosrae State from December 2003 through December 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Dec 2003 - May 2004
95%
Jun - Sep 2004
90%
Oct - Dec 2004
95%
source: UOG-WERI

Republic of Palau:  Conditions at Palau were wetter than anticipated during the first two quarters of 2003.  Copious amounts of rainfall continue to be experienced on Palau.  The 62.27 inches of rain at Koror during the third quarter of 2003 was the highest recorded rainfall during this quarter at any station in Micronesia (Figure 1a).  Rainfall at the Weather Service Office at Koror during July, August, and September was 25.03 inches (139%), 13.57 inches (91%), and 23.67 inches (200%), respectively.  The 3-month total of 62.27 inches was 139% of normal.  For the months of July, August, and September, the monthly rainfall distribution at Nekken Forestry was slightly drier overall than at the Weather Service Office in Koror with 18.64 inches (103%), 17.61 inches (118%), and 17.64 inches (149%).  Farther south at Peleliu, rainfall totals for July, August, and September were 20.23 inches (117%), 9.11 inches (61%), and 13.60 inches (115%) respectively.  

   Two tropical cyclones formed in Micronesia in the first three months of 2003, and passed well northeast of Palau:  Tropical Storm Yanyan in January and Super Typhoon Kujira in April.  Neither of these tropical cyclones had any major effect in Palau.  During June, July and August, Palau was affected by the beginning stages of typhoons Soudelor, Koni, Imbudo, and Etau.   The dominant effect of these tropical cyclones was periods of heavy rain showers.  During November 2003 Typhoon Lupit severely affected Yap State, but it was far enough away from Palau that there were no serious problems there.  

   Predicted rainfall for Palau from December 2003 through December 2004 is:
 
Inclusive Period
% of Long-Term Average
Dec 2003 - May 2004
100%
Jun - Sep 2004
95% 
Oct - Dec 2004
90% 
source: UOG-WERI

Republic of the Marshall Islands (RMI):  After abundant rainfall during most of 2002 in the central and southern RMI, the first quarter of 2003 saw near normal rainfall there.  Only in northern atolls, such as Kwajalein, Wotje, and Utirik did dry conditions set in late in 2002, and continue into the first quarter of 2003.  During the second and third quarters of 2003, however, near normal rainfall occurred throughout the RMI.  The Majuro weather station measured 10.15 inches (78%), 6.33 inches (55%), and 17.07 inches (137%) during July, August, and Septmber.  For the 3-month period, the total for Majuro was 91% of normal.  Rainfall at Kwajalein (and nearby Ebeye) was 10.03 inches (96%) in July, 10.54 inches (104%) in August, and 10.36 inches (88%) in September, for a three month total of 96% of normal.  

    After weak or moderate El Niño events (such as 2002), the rainfall at Majuro, Kwajalein and the northern islands of the RMI tends to be below normal, but at atolls south of 6°N it remains near normal.  The northern atolls of the RMI were one of the few regions in Micronesia where some extended periods of dry weather occurred during the first half of 2003.   

    As stated in earlier ENSO Updates, the threat of tropical cyclones was expected to be reduced in the RMI during 2003, since tropical cyclone activity shifted west as it typically does in the years that follow an El Niño.  So far in 2003, no numbered or named tropical cyclones have affected the RMI.  

   Predicted rainfall for the RMI from December 2003 through December 2004 is as follows:
   
Inclusive Period
% of Long-Term Average
---
       S. of 6°N        6°N to 8°N         N. of 8°N 
Dec 2003 - May 2004
            95%                 95%                    85%
Jun - Sep 2004
            95%                 90%                    95%
Oct - Dec 2004
            95%                 95%                    90%
source: UOG-WERI



APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 20 November 2003, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY:  issued by Climate Prediction Center/NCEP on December 11, 2003

   Surface and subsurface temperatures remained warmer than average across most of the equatorial Pacific Ocean during November. Equatorial ocean surface temperatures greater than +0.5°C (~1°F) above average were found in most areas between Indonesia and the South American coast. Departures greater than +1°C were found between 150°E and 170°W. Positive SST anomalies were observed in all four Niño index regions for the second consecutive month. However, the 850-hPa zonal wind indices, OLR index, 200-hPa zonal wind index, SOI and EQSOI all indicate ENSO-neutral conditions. Over the past few months these atmospheric indices have not shown any significant trends that would support either additional large-scale increases or any substantial decreases of SST anomalies in the equatorial Pacific.

   A majority of the statistical and coupled model forecasts indicate near-average conditions in the tropical Pacific (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) through Northern Hemisphere winter 2003-2004. However, some forecasts indicate that weak warm episode conditions will develop during the winter, which is consistent with observed trends in SST anomalies, particularly in the vicinity of the date line.

   The three-month (September-November) average SST anomaly in the Niño 3.4 region (+0.4°C) is just below the threshold (+0.5°C) required for NOAA to declare a weak Pacific warm episode (El Niño). It is likely that the October-December 2003 average will reach that threshold and that borderline weak El Niño / ENSO-neutral conditions will persist through the Northern Hemisphere winter of 2003-04. However, it seems unlikely that classical El Niño conditions will develop along the west coast of South America.

   In the past, weak Pacific warm episodes have not shown consistent temperature and precipitation impacts, especially for areas outside the tropical Pacific. Therefore, these conditions are not likely to have significant impacts on the wintertime temperature and precipitation patterns over the United States.

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)

Forecast Sea Level Anomaly (cm, 3-Mon. Average)

The full suite of Dr. Xue's model results is 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 (December 2003 - February 2004 and March - May 2004) 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  M. Lander at 671-735-2685 for  information on tropical cyclones and climate in the Pacific Islands.

NOAA National Weather Service-Pacific Region
WEATHER SERVICE FORECAST OFFICE (WSFO)
3232 Hueneme Road, Barrigada, Guam, 96913
Contact C. Guard at 641-472-0900 for further 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: peac@noaa.gov

Publication of the Pacific ENSO Update is supported in part by
the National Oceanic and Atmospheric Administration (NOAA),
National Weather Service-Pacific Region Headquartersunder contract
no. AB133W-02-SE-056.  The views expressed herein are those of the
author(s) and do not necessarily reflect the views of NOAA,
any of its sub-agencies, or cooperating organizations.
 

Back to Pacific ENSO Update - Home Page
.