Pacific ENSO Update

1st Quarter 2003-Vol. 9 No. 1


CURRENT CONDITIONS

    Recent climate anomalies in Micronesia and in the central Pacific indicate that the moderate El Niño of 2002 entered its mature phase by December, and is now beginning to weaken.  Although the El Niño of 2002 is now showing signs of weakening, it must be kept in mind that some effects of El Niño (e.g., drought in Micronesia) occur during the year after El Niño.  Fortunately, rainfall deficits from October 2002 through February 2003 in Micronesia have been nowhere near as large as in the same time period during 1997-1998.  A suite of international computer forecasts of El Niño are in general consensus that El Niño conditions in the Pacific basin will slowly weaken in the coming months.  The following ENSO diagnostic discussion was posted on the U.S. Climate Prediction Center web site on February 6, 2003; it states, in part:

    “Warm episode (El Niño) conditions continued during January 2003, as equatorial SST anomalies remained greater than +1°C in the central equatorial Pacific (175°E-125°W).  In addition, enhanced precipitation and cloudiness were observed over the central tropical Pacific, and positive subsurface temperature departures and a deeper-than-average oceanic thermocline were observed throughout the equatorial Pacific east of 180°W.  These conditions are consistent with mature warm episode conditions.  During January 2003 there were indications that the warm episode is beginning to weaken.  Sea surface temperature anomalies decreased throughout the eastern equatorial Pacific by as much as 1.5°C during the month, while equatorial easterly winds were near normal throughout the central and eastern equatorial Pacific.  Over the past several weeks there has also been a steady eastward progression of negative subsurface temperature anomalies, indicating a gradual depletion of the excess warmth in the upper ocean of the equatorial Pacific.  This evolution is typical during the mature phase of warm episodes.  Recent values of atmospheric and oceanic [ENSO] indices … are all considerably smaller in magnitude than those observed during the 1997-98 El Niño.  The warming associated with the current event has been greatest in the central equatorial Pacific . . . Regions farther east [nearer the South American Coast] have warmed much less.   A comparison with previous warm episodes in the last 50 years indicates that, for the equatorial Pacific as a whole, the current event is moderate in intensity.  Consistent with current conditions and recent observed trends, most coupled model and statistical model forecasts indicate that El Niño conditions will continue to weaken through April 2003.
    . . . Those areas of the world usually affected by El Niño may continue to experience related impacts during the next 2-3 months.”

    The rainfall during the calendar year of 2002 was near normal to wetter than normal throughout Micronesia and in American Samoa (Figure 1).  During 2002, many of the island groups of Micronesia experienced some extreme rain events related to tropical cyclones.  A disaster occurred at Chuuk on July 2 when Tropical Storm Chataan nearly passed over the island.  Rainfall amounts of almost 20 inches in 24 hours resulted in landslides that killed 47 people.  Chataan also affected Guam with up to 20 inches of rain in 24 hours.  Flood-levels of rivers in the south of that island were at historical highs.  Fortunately, no lives were lost on Guam when the winds and extreme rains of Chataan struck on the 5th of July.  During early December 2002, Typhoon Pongsona moved through Micronesia causing some damage on Chuuk, and major destruction on Guam.  Pongsona ranked among the top typhoons of the past century to hit Guam, in terms of wind intensity, short-term rainfall rates, and damage levels.
 
 

SST

    Sea surface temperatures (SSTs) across the tropical Pacific in December 2002 were generally warmer than normal, with a band of greater than +1°C persisting along the equator from about 175°E to the coast of South America.  The greatest SST anomaly of nearly +3°C was present along the equator at 160°W.  Since then, SST in the eastern equatorial Pacific has cooled.  During January maximum anomalies on the equator were approximately +1°C between 150°W and 180°.  The SST remains near normal to slightly cooler than normal throughout most of Micronesia.

    The temperature of the subsurface ocean water showed substantial warming in the far eastern Pacific during December.  It was generally at least 2ºC warmer than normal to a depth of about 150 meters in the equatorial Pacific from 180° eastward to the coast of South America.  Peak warm anomalies at depth occurred between 115°W to 95°W, where the temperature at 50-100 meters was over 5ºC warmer than normal.  Isotherms have shoaled in the equatorial western Pacific and subsurface waters are over 2°C colder than normal at 100 meter depth near 140°E.  There has also been a steady eastward progression of negative subsurface temperature anomalies, indicating a gradual depletion of the excess warmth in the upper ocean of the equatorial Pacific.  By January 2003, the warm subsurface waters in the eastern Pacific cooled slightly from their December values.  The current distribution of SST and subsurface water temperature anomalies are typical of mature El Niño conditions.
 
 

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 meters below the non-El Niño high stands of the sea.  The sea level drops to its lowest magnitude at the end of the El Niño year, and then rises quickly to above normal by May or June of the following year.  During 1999, 2000, and 2001, the sea level has been above normal in Micronesia.  By November 2002, the sea level had fallen in some places over 40 cm from its 1999 high point, and stood below normal at most locations.  The greatest lowering of the sea level (20 cm below normal) was observed in Palau and Yap (Figure 2).  The sea level fell to nearly 10 cm below normal values all the way eastward to the northern Marshall Islands.  Lowered sea level during El Niño causes the water level in shallow dug wells on atolls to fall, compounding the effects of diminished rainfall.   The sea level throughout Micronesia should recover to near normal values by May 2003.
 

SOI
    The Southern Oscillation Index (SOI) has now averaged near -1.0 since May 2002.  During May 2002 through January 2003, the SOI values were:  May (-1.2), June (-0.7), July (-0.7), August (-1.6), September (-0.7), October (-0.7), November (-0.6), December (-1.4), and January 2003 (-0.4).  Nearly all
El Niño events are associated with a persistently negative SOI.  The SOI should remain negative for the next few months, but the average value should rise to near zero by May or June 2003.
 
 

TROPICAL CYCLONE ACTIVITY

    During 2002, there were 31 tropical cyclones numbered by the Joint Typhoon Warning Center (JTWC) in Hawaii.  Of these, the Japan Meteorological Agency (JMA) named 23, and gave a name to an additional tropical cyclone that was not numbered by the JTWC.  Two hurricanes named by the Central Pacific Hurricane Center (CPHC) in Hawaii, moved into the western North Pacific as typhoons.   Western North Pacific tropical cyclone activity for 2002 included:  Tropical Storm (TS) Tapah (01W), Super Typhoon (STY) Mitag (02W), Tropical Depression (TD) 03W, TD 04W, STY Hagibis (05W), TS 06W, Typhoon (TY) Noguri (07W), STY Chataan (08W), TY Rammasun (09W), STY Halong (10W), TS Nakri (11W), STY Fengshen (12W), TS 13W, TS Fungwong (14W), TS Kalmaegi (15W), TS Kammuri (16W), TD 17W, TD 18W, STY Phanfone (19W), TS Vongfong 20W, TY Rusa (21W), TY Sinlaku (22W), TS Hagupit (23W), TS Changmi (no JTWC number), TS Mekkhala (24W), STY Higos (25W), TY Bavi (26W), TD 27W, TD 28W, TY Maysak (29W), TY Haishen (30W), and STY Pongsona (31W).  Also, for the first time since the 1997 El Niño, a tropical cyclone named by the CPHC in August 2002 – Ele (02C) – became a hurricane.  Ele crossed the date line and became a long-lasting typhoon in the subtropics of the western North Pacific.  Another hurricane named by the CPHC – Huko (03C)–  moved into the western Pacific and passed near Wake Island on November 5.

    During late December 2002 through February 2003, five tropical cyclones affected the south Pacific:  Zoe (06P), Ami (10P), Beni (12P), Cilla (13P), and Dovi (15P).  Zoe, with a peak intensity of 155 kt, was one of the most intense tropical cyclones ever observed in the South Pacific.  Zoe struck some of the islands in the Solomon’s, and many were feared dead, especially on two remote islands of Anuta and Tikopia where satellite imagery suggested that the brunt of this powerful tropical cyclone was felt.  Despite massive damage to crops and homes, no one on these islands was badly hurt, having managed to shelter on high ground.  In mid-January, Ami battered northern Fiji, bringing huge waves that smashed houses, destroyed crops and left two children missing and feared dead. Cyclone Ami moved across Vanua Levu, the country's second-biggest island, and the Lau group of 20 islands.  In mid-Febraury 2003, Dovi formed east of Samoa, and became one of the most intense tropical cyclones observed east of the International Date Line in many years.  According to the JTWC, Dovi reached a peak intensity of 135 kts.  A greater than average number of tropical cyclones in the south Pacific is typical of the period December through June of the year after El Niño.  Effects of El Niño on tropical cyclones in the Southern Hemisphere include a greater than normal number of tropical cyclones in the South Pacific (with some of these becoming very intense), and a higher probability that some of the tropical cyclones of the South Pacific will form east of the International Date Line.

    In summary, during 2002 there were 24 tropical cyclones named by the JMA.  The JTWC rated 25 tropical cyclones at tropical storm intensity or higher.  This does not include the two tropical cyclones that moved into the western North Pacific from the central North Pacific, and the five tropical depressions numbered by the JTWC.  Using the JTWC statistics, the 27 tropical cyclones of tropical storm intensity or higher was close to the average of 28.  There were 17 typhoons (one short of the average of 18), and 7 super typhoons (3 greater than the average of 4).

    Many of the islands of Micronesia were adversely affected by tropical cyclones in 2002.  When it was still a typhoon, Super Typhoon Mitag passed through Yap State in March, causing substantial damage.  Super Typhoon Chataan was a costly and deadly typhoon for Micronesia.   Passing first through Chuuk State as a tropical storm, its heavy rains caused landslides that killed 47 people in Chuuk.  Chataan passed directly over Guam on the 5th of July and caused extensive damage.  Super Typhoon Pongsona passed through the northern atolls of Chuuk State in early December, causing some damage (mostly from high surf).  Pongsona later passed directly over Guam causing widespread destruction.  Many other tropical cyclones in 2002 began in Micronesia, contributing to abundant rainfall.  Typical of an El Niño year, many of the year’s tropical cyclones formed in Micronesia from Pohnpei State eastward to the Marshall Islands.

    El Niño years have a near normal to a slightly above normal number of tropical cyclones in the western North Pacific.  There tends to be an increase in the number of intense typhoons in an El Niño year.  This has been reflected in the seven super typhoons that occurred.  Another factor to consider is that during El Niño (even a weak event), the formation region 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 increases 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 March through mid-July (this occurred with eight tropical cyclones affecting Micronesia through mid-July).  During the year after El Niño, the threat of tropical cyclones in most of Micronesia returns to near normal, unless the Pacific climate progresses to La Niña conditions, in which case, the formation region of tropical cyclones tends to shift to the west and reduces the threat of tropical cyclones from Guam eastward.  The threat of tropical cyclones is expected to return to normal for 2003 in all of Micronesia.



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: January 2003 saw a third consecutive dry month overall in the State of Hawaii consistent with continuing El Niño conditions across the Pacific. Noteworthy aspects of the month’s weather included only three days of trade wind weather and a large number of frontal systems affecting the island chain. A total of seven cold fronts and shear lines reached the islands (2 January, 4-5 January, 10-11 January, 15-16 January, 19-20 January, 24-26 January, and 29-31 January). Most of these were fast-moving systems lacking significant upper level support, with both factors combining to prevent substantial rainfall accumulations over any specific area.  Significant effects from these weather systems were mainly in the form of damaging winds from localized amplification of strong southwesterly low-level flow to the east of the frontal boundaries.

    The exception was the frontal passage of 29-31 January. After pushing across Kauai and Oahu as a weak and complex frontal system, the cold front stalled near the island of Maui. Its remnant moisture helped produce heavy showers over the northeast-facing slopes of Maui County and Oahu. Minor flooding was reported in the Kahului area of Maui and the Punaluu, Hauula, and Kaneohe areas of Oahu. No injuries or significant damages were reported from this event.

Kevin Kodama-Senior Service Hydrologist, NWSFO Honolulu, Hawaii



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

American Samoa:  Rainfall at Pago Pago Airport for October, November, and December was 11.87 inches (108%), 15.26 inches (141%), and 7.94 inches (55%), respectively, amounting to 96% of normal for the 3-month period.  The total rainfall in 2002 of 112.80 inches was 93% of the normal annual total of 121.80.  There was high month-to-month variability with heavier than normal rainfall during most of the first half of 2002.  The very dry September with only 1.62 inches was one of the driest months at Samoa in several years.  Abundant rains returned to American Samoa during October, whereas at the start of the rainy season, the December total of 7.94 inches was about half of normal.  The January 2003 rainfall total of 7.41 inches was also only about half of normal.  Indications are that February 2003 is also running below normal.

    Rainfall in American Samoa is not as closely tied to ENSO as it is in other regions of the Pacific.  However, some prolonged very dry periods in 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.  Yet, 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.  The 2002 El Niño was moderate, so a prolonged dry period is not expected anytime in 2003.  However, December and January were quite dry, so if the rainfall in February, March, or April (three of the wettest months along with December and January) is well below average, American Samoa will suffer a substantial net loss of rain.

    With the onset of El Niño in 2002 (although only moderate), the risk of a damaging tropical cyclone may increase for Samoa through March 2003.

    Predicted rainfall for American Samoa from March 2003 through February 2004 is:
 
Inclusive Period
% of Long-Term Average
Mar 2003 - May 2003
80%
Jun 2003 -Sep 2003
85%
Oct 2003 - Feb 2004
95%
source: UOG-WERI

Guam/CNMI:  Rainfall at Guam International Airport (GIA) during October, November, and December was 7.02 inches (58%), 6.94 inches (85%), and 25.73 inches (477%), respectively, amounting to 155% of normal for the 3-month period.  For 2002, the total rainfall of 139.10 inches was 153% of the normal annual total of 90.98.  At GIA the annual total of 139.10 inches is the second highest annual total ever recorded there, exceeded only by the 141.12 inches recorded in 1976.  There was high month-to-month variability with extremely heavy rainfall totals in July and December (due in large measure to typhoon passages).  Andersen Air Force Base (AAFB) measured 6.26 inches (49%), 6.95 inches (76%), and 24.98 inches (418%), or 137% of the average rainfall for October-December.  The 2002 annual total at AAFB was 132.10 inches (134% of normal), and is the second highest total on record there, exceeded only by the 151.60 inches recorded in 1976.   Nearly 30 inches (21%) of Guam’s annual rainfall in 2002 was derived from typhoons Chataan and Pongsona.  Typhoon Chataan struck Guam on July 5, 2002 bringing destructive winds and very heavy rainfall.  On December 8, 2002, an even more powerful typhoon — Typhoon Pongsona — passed over Guam bringing devastating high winds and very heavy rainfall.  Power, water and phone service were disrupted for over two months.  Final damage estimates may exceed $700 million.

    Rainfall at the Saipan International Airport (SIA) for October, November and December was 4.30 inches (40%), 5.67 inches (98%), and 10.43 inches (271%), or 100% of the average for the period.  For the same months, Capitol Hill’s measured rainfall was similar to the airport with 6.03 inches (50%) in October, 7.87 inches (108%) in November, and 7.90 inches (165%) in December.  The 2002 annual total of 73.92 inches was 100% of normal.  Capitol Hill’s 2002 annual rainfall of 95.85 inches of rain was the highest recorded during 2002 among all Saipan stations, followed by the 89.88 inches recorded at Mt. Tagpochau.

     Rainfall amounts for October, November, and December at the Tinian Airport were 7.69 inches (64%), 5.50 inches (75%), and 5.00 inches (104%), respectively.  The 3-month rainfall for Tinian Airport was below normal at 75%.  The 2002 annual total of 81.63 inches was near normal at 98%.  At Rota Airport, October, November, and December rain amounts were 7.13 inches (56%), 5.39 inches (68%), and 7.49 inches (132%), respectively.  This gave a 3-month average of 74%.  The 2002 annual total of 107.23 inches was quite high at 113% of normal.

    Based on 30 years of rainfall data, El Niño years on Guam and the CNMI average slightly wetter than normal.  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.  Now, in early 2003, the El Niño event of 2002 has entered its mature phase.  The rainfall on Guam and in the CNMI was drier than normal in October and November, but the rains from Typhoon Pongsona pushed the December totals above normal.  January 2003 was dry on Guam, but rains from Tropical Storm YanYan helped to keep the totals in the CNMI above normal.  Persistent dryness is still expected to occur from March through the start of the rainy season in July.  The threat of typhoons for Guam and the CNMI should be normal during 2003.

   Predicted rainfall for the Mariana Islands from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
---
      Guam/Rota                                              Saipan/Tinian
    Mar 2003 -May 2003
           50%                                                          50%
Jun 2003 - Jul 2003
           70%                                                          65%
 Aug 2003- Oct 2003 
           90%                                                          90%
Nov 2003-Feb 2004
           95%                                                          95%
source: UOG-WERI

Yap State:  Stations on the main island of Yap were wet during October, and then began to dry out in the final two months of 2002, and January 2003.  The atolls of Yap State all began to experience dry conditions from October 2002 through January 2003.  The Weather Service Office near the Yap Airport recorded 13.91 inches (116%) in October, 6.51 inches (72%) in November, and 5.42 inches (69%) in December, or 86% of normal rainfall for the three months.  The 2002 annual total at the Yap WSO was 151.22 inches or 109% of normal.  Rainfall amounts on Ulithi were 6.37 inches (63%) in October, 5.62 inches (73%) in November, and only 1.83 inches (24%) in December, or 54% for the 3-month period.  The 2.50 inches at Ulithi in January 2003 were well below (40%) normal.  The 2002 annual total at Ulithi was 98.07 inches or 96% of normal.  Farther south at Woleai Atoll (which is normally wetter than Yap and Ulithi year-round), persistent dryness also set in from October 2002 through January 2003.  The rainfall was 6.45 inches (47%) in October, 8.40 inches (78%) in November, and 7.62 inches (67%) in December, for a 3-month average of 64%.  The 3.90 inches at Woleai in January 2003 was well short (36%) of normal.  El Niño years at Yap average slightly wetter than normal for the first nine months, then dryness begins in the fall.  This has occurred.  The very dry conditions that follow an El Niño year tend to start in November and carry into the year following El Niño. The persistent dryness that set in late in the El Niño year 2002 should continue through the first half of 2003 (the post-El Niño year).  Tropical cyclone activity had an early start in Yap State during 2002 with the passage of Mitag in early March, and a brush by the developing Rammasun in late June.  The tropical cyclone threat should return to normal in 2003.

   Predicted rainfall for Yap State from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Mar 2003 - Apr 2003
  50% 
May 2003 - Jun 2003
   70% 
Jul 2003 - Oct 2003
    95% 
Nov 2003 - Feb 2004
     90% 
source: UOG-WERI

Chuuk State:    Most of the islands and atolls of Chuuk State began to experience dry conditions from October through December 2002.  January 2003, however, was relatively wet, in part because of the passage of the tropical disturbance that became Tropical Storm Yanyan.  During October, November, and December, the Weather Service Office at Weno Island measured 7.76 inches (58%), 7.85 inches (76%), and 10.24 inches (94%).  This amounted to 75% of normal for the 3-month period.  The January 2003 rainfall of 10.06 inches at WSO Weno was 94% of normal.  The 2002 annual total at WSO Weno was a very wet 171.05 inches or 127% of normal.  At Xavier High School (also on the island of Weno) the October, November, and December rainfall was 6.45 inches (48%), 8.40 inches (81%), and 7.62 inches (70%), respectively.  The 2002 annual total at Xavier High School of 151.22 inches was 113% of normal.  These very wet conditions were largely the result of a persistent monsoon trough stretching through the Caroline Islands throughout the spring, summer and fall; and from heavy rainfall from tropical cyclones passing near the island – most notably, Chataan.  A persistent monsoon trough in the Caroline Islands from spring into the summer months is typical for an El Niño year.  It was somewhat drier for most of 2002 in the Mortlocks and at Polowat, which did not experience the heavy rains of Chataan.  For example, at Lukunoch, rainfall for October, November, and December was 4.50 inches (33%), 7.45 inches (72%), and 11.76 inches (108%) for the respective months.   The totals at Polowat for October and December were 5.89 inches (49%) and 5.26 inches (57%).  The 2002 annual rainfall totals at Lukunoch and Polowat were 119.68 inches (89%) and 105.23 inches (87%), respectively.

   Rainfall throughout most of Chuuk State became persistently drier than normal beginning in October as the effects of the 2002 El Niño set in.  Along with reduced rainfall, the sea level became lower than normal.  The lowered sea level associated with El Niño should persist until March.  In addition to reduced rainfall, lowered sea level also causes the water level in shallow dug wells to drop.  This is especially a problem on the atolls.  Tropical cyclones have continued to affect Chuuk State through January 2003. The threat from tropical cyclones should be normal for the rest of 2003.

   Predicted rainfall  for Chuuk State from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Mar 2003 - Apr 2003
  50% 
May 2003 - Jun 2003
  75% 
Jul 2003 - Oct 2003
   90% 
Nov 2003 - Feb 2004
   85% 
source: UOG-WERI

Pohnpei State:  With the notable exception of Kapingamarangi, the islands and atolls of Pohnpei State began to experience drier than normal conditions in the months of October 2002 through January 2003.  Close to the equator, at Kapingamarangi, the October 2002 through January 2003 rainfall total was wetter than normal.  Convection along the equator and enhanced monsoonal westerlies have kept Kapingamarangi in rainfall surpluses for almost every month since April 2001.  The highest measured rainfall total at any station in Pohnpei State during 2002 was the 184.52 inches (98% of normal) recorded at the weather station at Kolonia.  The greatest departure from normal at any station in Pohnpei State during 2002 was at Kapingamarangi, where the annual total of 143.95 inches was 131% of normal.  The monsoon trough was persistent across the Caroline Islands during spring through summer 2002 with several episodes of southwesterly wind and heavy rain showers.  Several tropical disturbances and the beginning stages of named tropical cyclones affected Pohnpei State in 2002.   At the Kolonia Weather Service Office, the October, November, and December rainfall totals were 7.64 inches (46%), 14.81 inches (94%), and 8.34 inches (135%), respectively.  This amounted to a 3-month total of 30.79 inches or only 65% of average precipitation.  The 2002 annual total of 184.52 inches of rain at WSO Kolonia was 98% of normal.  The January 2003 rainfall total of 10.71 inches at WSO Kolonia was 82% of normal.  At Pingelap, observed rainfall in October, November, and December was 11.16 inches (75%), 8.39 inches (55%), and 4.28 inches (31%), respectively, for a 3-month amount of 56%.  At Nukuoro, October through December precipitation amounts were 8.90 inches (83%), 8.64 inches (72%), and 11.40 inches (95%), respectively, for a 3-month amount of 83%.  Kapingamarangi picked up a substantial amount of rain during October through December 2002 with totals of 9.40 inches (195%), 15.25 inches (186%), and 3.56 inches (41%) for the three months.  The January 2003 rainfall total at Kapingamarangi was 14.57 inches, or 139% of normal.  The 2002 annual total rainfall at Kapingamarangi was 143.95 inches, or 139% of normal.

   Rainfall throughout most of Pohnpei State (except for Kapingamarangi) became persistently drier than normal beginning in October as the effects of the 2002 El Niño set in.  Along with reduced rainfall, lowered sea level associated with El Niño will persist until March.  Both factors cause the water level in shallow dug wells to drop.  This is especially a problem on the atolls.  Tropical cyclones and several tropical disturbances that later became named tropical cyclones affected Pohnpei State through most of 2002.  Even in January 2003 portions of Pohnpei State were affected by an area of disturbed weather associated with the developing Tropical Storm Yanyan.  The threat of tropical cyclones should be normal in 2003.

   Predicted rainfall for Pohnpei State from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
--- 
Pohnpei Islands and atolls            Kapingamarangi
Mar 2003 - Apr 2003
             55%                                     85%
May 2003 - Jun 2003
             75%                                     80%
Jul 2003 - Sep 2003
             90%                                     80%
Oct 2003 - Feb 2004
             85%                                     85%
source: UOG-WERI

Kosrae State:  Stations on Kosrae experienced a small decrease in rainfall totals during October through December 2002, and near normal rainfall in January 2003.  Dryness associated with El Niño has not appreciably affected Kosrae State yet.  Several tropical disturbances and persistent convection at low latitudes near the international date line continued to affect Kosrae and the southern RMI through the end of 2002 and in January 2003.  Rainfall at Kosrae (SAWRS) during October, November, and December was 12.98 inches (80%), 16.54 inches (104%), and 13.32 inches (92%) respectively.  The 3-month total of 42.84 inches was 92% of the normal total of 46.60 inches.  The 2002 annual total of 224.06 was 109% of normal.  Only one other Kosrae station (among four) had a higher annual total, and this was the 228.11 inches recorded at Tafunsak. The Kosrae rain totals were the highest recorded values in all of Micronesia in 2002 (Figure 1a).   A summary of the four Kosrae stations shows: (1) October through December rain totals of 42.84 inches at SAWRS, 40.73 inches at Tafunsak, 43.81 inches at Tofol, and 35.58 inches at Utwa; and, (2) 2002 annual totals of 224.06 inches at SAWRS, 185.66 inches at Tafunsak, 228.11 inches at Tofol, and 199.45 inches at Utwa.

   Rainfall for Kosrae State is expected to become persistently drier than normal beginning in March 2003 as the effects of the 2002 El Niño set in.  The threat posed by tropical cyclones to Kosrae will be normal during 2003.

   Predicted rainfall for Kosrae State from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Mar 2003 - Apr 2003
60%
May 2003 - Jun 2003
75%
Jul 2003 - Sep 2003
90%
Oct 2003 - Feb 2004
                                  85%
source: UOG-WERI

Republic of Palau:  Conditions at Palau were drier than normal at most locations during the fourth quarter of 2002, and have been since the summer months.  Rainfall at the Koror Weather Service Office during October, November and December was 8.70 inches (63%), 13.01 inches (115%), and 6.07 inches (51%), respectively.  The 3-month average was 75% of normal.  For October, November and December, the monthly rainfall distribution at Nekken Forestry was similar to that at the Weather Service Office in Koror with only 8.86 inches (64%), 11.99 inches (107%), and 8.62 inches (72%).  Farther south at Peleliu, rainfall totals for October through December were 6.41 inches (46%), 7.40 inches (65%), and 7.44 inches (62%), respectively.  During January 2003, rainfall at most locations in the Republic of Palau was near normal to slightly below normal with amounts of 8.88 inches (83%), 9.58 inches (90%), 10.40 inches (97%), and 7.18 inches (67%) at WSO Koror, Mariculture, Nekken, and Peleliu respectively.  The 2002 annual total was 130.80 inches (88%) at WSO Koror, and 111.83 inches (76%) at Nekken.

   El Niño years at Palau average near normal through July, then dry conditions set in for an extended period.  The very dry conditions associated with El Niño tend to set it in as early as September of the El Niño year and carry into the summer of the following year.  In keeping with El Niño in 2002, some tropical cyclones formed in Micronesia and passed near Palau early in the year:  Tropical Storm Tapah in January, Super Typhoon Mitag in early March (which caused some minor property damage in parts of Palau), Tropical Depression 03W in mid-March, and Typhoon Rammasun in late June.  Tropical cyclone activity shifted eastward late in 2002, and Palau was not threatened by a tropical cyclone during the final few months of the year.  The threat of tropical cyclones will be normal for 2003.

   Predicted rainfall for Palau from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
Mar 2003 - Apr 2003
50%
May 2003 - Jun 2003
75% 
Jul 2003 - Sep 2003
90% 
Oct 2003 - Feb 2004
95% 
source: UOG-WERI

Republic of the Marshall Islands (RMI):  Abundant rainfall in the second and third quarters of 2002 continued to occur in the central and southern RMI during the fourth quarter of 2002.  Only in northern atolls, such as Kwajalein and Wotje, did dry conditions set in late in the year.  The abundant rains in the RMI throughout much of 2002 were associated with several tropical disturbances and other mesoscale convective features at the eastern end of the monsoon trough.  Later in the year El Niño-related deep convection persisted at low latitudes near the international date line, keeping the central and southern Marshalls wet.  The Majuro weather station measured 15.28 inches (110%), 8.79 inches (68%), and 17.41 inches (147%) during October, November and December, respectively.  For the 3-month period, the average for Majuro was 109% of normal.  Rainfall at Kwajalein (and nearby Ebeye) was 12.09 inches (102%) in October, 3.80 inches (36%) in November, and 6.38 inches (84%) in December, for a 3-month average of 73%.  The 2002 annual rainfall totals at Majuro and Kwajalein were 144.92 inches (110%) and 105.00 inches (102%) respectively.

   A moderate El Niño occurred in 2002.  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 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.  During 2002, tropical cyclone activity shifted east of normal in the western North Pacific basin.   Many tropical disturbances moved through the RMI, some of which later moved west and became named tropical cyclones.  The tropical cyclone threat for the RMI should be near normal during 2003.

   Predicted rainfall for the RMI from March 2003 through February 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
---
       S. of 6°N        6°N to 8°N         N. of 8°N 
Mar 2003 - Apr 2003
            75%                 50%                    40%
May 2003 - Jun 2003
            75%                 70%                    50%
Jul 2003 - Sep 2003
            95%                 95%                    90%
Oct 2003 - Feb 2004
            90%                 95%                    85%
source: UOG-WERI



APPENDICES:

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

ENSO ADVISORY:  issued by Climate Prediction Center/NCEP on February 6, 2003

         Warm episode (El Niño) conditions continued during January 2003, as equatorial sea surface temperature (SST) anomalies remained greater than +1°C in the central equatorial Pacific (175°E-125°W). In addition, enhanced precipitation and cloudiness were observed over the central tropical Pacific, and positive subsurface temperature departures and a deeper-than-average oceanic thermocline were observed throughout the equatorial Pacific east of 180°W.  These conditions are consistent with mature warm episode conditions.

   During January 2003 there were indications that the warm episode is beginning weaken. Sea surface temperature anomalies decreased throughout the eastern equatorial Pacific by as much as 1.5°C during the month, while equatorial easterly winds were near normal throughout the central and eastern equatorial Pacific. Over the past several weeks there has also been a steady eastward progression of negative subsurface temperature anomalies, indicating a gradual depletion of the excess warmth in the upper ocean of the equatorial Pacific. This evolution is typical during the mature phase of warm episodes.

   Recent values of atmospheric and oceanic indices, such as the SOI, 850-hPa wind index, Niño 3.4, Niño 3,
Niño 1+2 are all considerably smaller in magnitude than those observed during the 1997-98 El Niño.  The warming associated with the current event has been greatest in the central equatorial Pacific (Niño 4 and Niño 3.4 regions). Regions farther east (e.g., Niño 3 and especially Niño 1+2) have warmed much less. A comparison with previous warm episodes in the last 50 years indicates that, for the equatorial Pacific as a whole, the current event is moderate in intensity.

   Consistent with current conditions and recent observed trends, most coupled model and statistical model forecasts indicate that El Niño conditions will continue to weaken through April 2003. Thereafter, the consensus forecast is for near-normal conditions during May-October 2003. Those areas of the world usually affected by El Niño may continue to experience related impacts during the next 2-3 months.
 

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 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 (March  - May 2003 and June - August 2003) 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: rsschnei@.hawaii.edu

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.
 

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