Pacific ENSO Update

2nd Quarter 2003-Vol. 9 No. 2


CURRENT CONDITIONS

    Recent climate anomalies in Micronesia and in the central Pacific indicate that the moderate El Niño of 2002 has ended.  Widespread drought tends to occur in Micronesia during the year after El Niño, and substantial rainfall deficits were expected throughout Micronesia during the first half of 2003.  Although some of the atolls of Yap State, Chuuk State and the Republic of the Marshall Islands (RMI) have been quite dry, many islands have received adequate rainfall.  Rainfall at Kosrae State and Pohnpei State, southern Chuuk State, and the Republic of Palau has been heavier and more frequent than expected.  Thus, expected moderate drought conditions at these locations will not materialize with this current ENSO event.  While we still expect some extended periods of dry weather throughout the region (even in equatorial areas), they will not be extensive enough to cause serious drought conditions before seasonal rains return.  Continued conservation measures may still be needed for the northern Marshall Islands into June.

    Residual warm ocean surface water in the equatorial region near the international date line has been associated with persistent deep convection in the southern RMI.  Areas of deep convection have continued to form in Micronesia from Palau east to the RMI, giving those areas some periods of heavy rain showers.  Two tropical cyclones, Tropical Storm Yanyan and Super Typhoon Kujira, affected parts of Micronesia in January and April, respectively.  Throughout all of Micronesia, rainfall deficits from October 2002 through March 2003 have been nowhere near as large as in the same period during 1997-98.  A suite of international computer forecasts of El Niño are in general consensus that El Niño conditions in the Pacific basin have ended, and 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.  The following ENSO Forecast Forum was posted on the U.S. Climate Prediction Center web site on April 10, 2003:

    “Warm episode (El Niño) conditions continued to weaken during March 2003, as the equatorial easterlies strengthened and SST anomalies decreased throughout the eastern and central equatorial Pacific. Since December, SST anomalies have decreased by more than 2°C in the eastern equatorial Pacific between 130°W and the South American coast. This decrease has resulted in near normal or slightly below normal SSTs in the region east of 120°W since February. During the same period there has also been a steady February. During the same period there has also been a steady decrease in the magnitude and extent of the positive subsurface temperature anomalies, indicating a depletion of the excess warmth in the upper ocean of the equatorial Pacific. This evolution is typical during the decay phases of warm episodes.
    A comparison of the 2002-03 El Niño episode with previous events in the last 50 years indicates that for the equatorial Pacific as a whole the 2002-2003 event was moderate in intensity. The SST departures associated with the event were greatest in the central equatorial Pacific … and least in the eastern equatorial Pacific. This pattern of anomalous warming, combined with the rapid weakening of the event, had a generally weaker than expected influence on the atmospheric circulation and hence the precipitation and temperature patterns over North and South America during January - March 2003 [As well as on the rainfall throughout Micronesia].
    Consistent with current conditions and recent observed trends, a majority of the coupled model and statistical model forecasts indicate that near-normal conditions will prevail through September 2003. …”
 
 

SST

    El Niño conditions continued to weaken during March 2003 as sea surface temperature (SST) anomalies again decreased across the equatorial Pacific.  SSTs remained more than 1°C above normal in the central Pacific between 170°E and 140°W, but were slightly cooler than normal east of 120°W.  SST anomalies across the central and eastern equatorial Pacific have steadily decreased since reaching maximum values in late 2002.  The SST remains near normal throughout most of Micronesia.

    Consistent with weakening El Niño conditions, the depth of the equatorial oceanic thermocline during March remained near normal across the central Pacific and was slightly below normal in the eastern Pacific. Ocean temperatures at thermocline depth (50-100 m) were 1-2°C above normal in the central equatorial Pacific and 2-4°C below normal in the eastern Pacific.  The temperature of the subsurface ocean water is now substantially cooler since its peak warmth in December 2002.  At peak warmth the subsurface water was generally at least 2ºC warmer than normal to a depth of about 150 meters in the equatorial Pacific from 180° east to the coast of South America.  Areas between 115°W to 95°W experienced warm anomalies of over 5°C warmer than normal at depths of 50-100 meters.  By March 2003, the area of subsurface water temperature anomalies in excess of +2°C had contracted.  It was found at 50-100 meter depth at the equator in two small regions: to the south-southeast of Hawaii, and to the south of Pohnpei.  Subsurface waters have become over 3°C colder than normal at 50-100 meter depth between 95°W and 120°W.  The subsurface water is also over 2°C colder than normal at 50-100 meter depth along the equator to the south of Pohnpei and Chuuk States.  The current distribution of SST and subsurface water temperature anomalies indicate that El Niño has ended.
 
 

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 the years 1999, 2000, and 2001, the sea level was 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 from its 1999 high point.  The greatest lowering of the sea level (20 cm below normal) was observed in Palau and Yap.  The sea level fell to nearly 10 cm below normal values 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 (Figure 2).  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, and rise slightly above normal during the second half of 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), January 2003 (-0.4), February (-1.2), and March (-1.0).  Nearly all El Niño events are associated with a persistently negative SOI.  When El Niño is over the SOI usually rises.  The SOI should slowly rise for the next few months, and be near zero by June or July 2003.
 
 

TROPICAL CYCLONE ACTIVITY

    During the first three months of 2003, there was one tropical cyclone in the western North Pacific that was numbered by the Joint Typhoon Warning Center (JTWC) in Hawaii.  The Japan Meteorology Agency (JMA) named it Yanyan.  Tropical Storm Yanyan formed near Pohnpei in mid-January and traveled toward Guam, giving the residents a scare so soon after the devastation wrought by Typhoon Pongsona in December 2002.  During April 2003, a very powerful tropical cyclone, Super Typhoon Kujira formed near Pohnpei and tracked to the south of Guam.  On Pohnpei, a young man died when high winds toppled a tree onto him.  A few days before the passage of the cyclone, a boat capsized in rough seas resulting in a drowning death.  Flooding in Kolonia from heavy rains was reported by residents to have been the worst in 60 years.  After affecting Pohnpei, this typhoon moved westward passing first to the north of Chuuk and later to the south of Guam; these locations were largely spared any damaging effects.

   During late December 2002 through April 2003, nine tropical cyclones affected the South Pacific:  Zoe (06P), Ami (10P), Beni (12P), Cilla (13P), Dovi (15P), Erica (22P), Craig (24P), Eseta (25P) and Tropical Cyclone 27P.  Zoe, with a peak intensity of 155 kts, was one of the most intense tropical cyclones ever observed in the South Pacific.  Zoe struck some of the islands in the Solomon’s.  Many were feared dead, especially on the two remote islands of Anuta and Tikopia.  Satellite imagery suggested these islands felt the brunt of this powerful tropical cyclone.  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 the top of Vanua Levu, the country’s second-biggest island, and the Lau group of 20 islands.  In mid-February 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.  In March three more tropical cyclones formed in the South Pacific – Erica, Craig, and Eseta.  Erica attained a very high intensity of 140 kts just as it crossed the island of New Caledonia where it caused millions of dollars in damages to infrastructure, killed two, and injured nearly a hundred. At the same time, Eseta formed to the east of Erica and passed to the south of Fiji with a peak intensity of 115 kts.  In Nuku’alofa, Tonga’s disaster management office said two tourist resorts in the western district of Tongatapu were almost completely destroyed by Cyclone Eseta.  Craig formed in the Gulf of Carpentaria  and dissipated over land in the far northeast of Australia.  In mid-April, another tropical cyclone (27P) moved south to the east of Fiji.  A higher than average number of tropical cyclones in the South Pacific is typical from December through June of the year after El Niño.  As in the western North Pacific, the effect of El Niño on tropical cyclones in the South Pacific is to allow more tropical cyclones to form farther east than normal.

   Since 2000, the Laboratory for Atmospheric Research (LAR) at City University of Hong Kong (Professor Johnny C.L. Chan, Chair and Dean) has been issuing real-time predictions of the annual number of tropical cyclones affecting the western North Pacific and the South China Sea (http://aposf02.cityu.edu.hk/~mcg/staff/staff.htm).  For predictions for the entire western North Pacific, different predictors give rather similar forecasts: it is unlikely that 2003 will see above-normal tropical cyclone activity over the entire western North Pacific.  The final forecasts call for a normal to below normal number of tropical cyclones (two less than normal), as well as typhoons (one less than normal).  Another group (http://Tropicalstormrisk.com), led by Dr. Mark Saunders at the Benfield Greig Hazard Research Centre, University College London has issued a prediction for a slightly more active season than normal in the western North Pacific with one more typhoon and one more intense typhoon than average.  These two forecasts are actually in close agreement that the tropical cyclone activity in the western North Pacific during 2003 will be near 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: The trade winds, largely absent during March, prevailed over the Hawaiian Islands during most of April. Several upper level lows helped destabilize the airmass over the island chain during the first 2 weeks of the month with heavy rains and thunderstorms observed on several islands.
   The most significant rain event occurred on 10 April over eastern Maui when an upper level low helped produce thunderstorms over the eastern slopes of Haleakala on the island of Maui. Flash flooding in Kipahulu Gulch, described as a 6 ft surge of water, caused the deaths of 2 tourists as they crossed a stream. No significant damages were reported with this event.

    A persistent upper level low also helped trigger heavy showers over Kauai and Oahu from 4 through 7 April. Advisories for minor flooding were issued for Oahu on 4, 6, and 7 April though no damages or injuries were reported.

    Fresh to strong trade winds persisted over the state from 12 to 24 April bringing numerous showers to the eastern slopes of the Big Island. The heaviest rains occurred on 20 April with 2 to 4 inches recorded by gages in the Hilo and Puna areas. Flood advisories were issued for minor flooding but no significant damages or injuries were reported.

Kevin Kodama-Senior Service Hydrologist, NWSFO Honolulu, Hawaii



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

American Samoa:  Rainfall at Pago Pago Airport for January, February, and March was 7.41 inches (59%), 9.11 inches (71%), and 10.41 inches (92%), respectively, amounting to 74% of normal for the 3-month period.  Above normal rains occurred at American Samoa during October and November 2002.  Since then, every month has had below normal rainfall.

    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; but 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 December 2002 through March 2003 was persistently drier than normal, a prolonged period of very dry conditions is not expected in 2003. American Samoa has passed through its period of greatest tropical cyclone activity without being affected by any cyclone.  For the remainder of 2003, the risk of a damaging tropical cyclone in American Samoa is very low.

    Predicted rainfall for American Samoa from May 2003 through April 2004 is:
 
Inclusive Period
% of Long-Term Average
May 2003 - Sep 2003
80%
Oct 2003 - Apr 2004
90%
source: UOG-WERI

Guam/CNMI:  Due in part to recent typhoons and low rainfall Guam features stubby and/or leafless wind-blasted trees and dry brown hillsides.  There are many areas (especially in the south) where wildfires have scorched the terrain.  Rainfall at Guam International Airport (GIA) during January, February, and March was 2.45 inches (43%), 3.13 inches (60%), and 5.40 inches (132%), respectively, amounting to 73% of normal for the 3-month period.  High spatial variation of rainfall totals occurred across Guam.  This was  especially true during March when a small-scale convective rain event affected the airport (2.03 inches of rain fell on the 11th), but not other locations (only a trace was recorded at the University of Guam on the 11th).  Andersen Air Force Base (AAFB) measured 4.94 inches (87%), 4.05 inches (78%), and 3.47 inches (85%), or 83% of the average rainfall for January-March.  The rain gage network at the University of Guam was one of the driest places on the island during the first quarter of 2003 with 2.58 inches (58%), 3.35 inches (90%), and 1.60 inches (54%) during January, February, and March, respectively.  On April 15, 2003, powerful Typhoon Kujira passed about 170 miles south of Guam bringing gusty winds and hazardous surf.  The typhoon did not cause any significant damage on Guam.  Southern sections of the island received some beneficial rains.

   The first quarter 2003 rainfall at Saipan and Tinian was higher (in terms of percent of normal) than anywhere else in Micronesia (Figure 1b).  The expected post-El Niño drought failed to materialize in the CNMI.  Although it is the dry season in the CNMI, Saipan and Tinian boast lush healthy forests, and roadside grasses that are tall, thick, and green.  Rainfall at the Saipan International Airport (SIA) for January, February and March was 5.52 inches (172%), 2.93 inches (122%), and 1.82 inches (91%), or 135% of the average for the period.  As on Guam during the first quarter of 2003, there was wide variation in the rainfall from place to place.  For example, Capitol Hill’s measured rainfall was much higher than the amount recorded at the airport with 10.86 inches (272%) in January, 4.74 inches (158%) in February, and 5.41 inches (216%) in September.

   Rainfall amounts for January, February, and March at the Tinian Airport were 4.01 inches (100%), 5.51 inches (184%), and 6.69 inches (268%), respectively.  The 3-month rainfall for Tinian Airport was well above normal at 171%.  As on Saipan, Tinian forests and grasslands appear as if well-watered.  At Rota Airport, January, February and March rain amounts were 6.29 inches (119%), 5.40 inches (116%), and 1.92 inches (52%), respectively.  This gave a 3-month average of 100%.  Parts of the western half of Rota still show effects of the wind blasting from Typhoon Pongsona in December 2002.

   The very dry conditions that follow an El Niño year tend to start in November and carry 4-7 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 has not materialized.  The fall 2002 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.  Guam has been somewhat dry through March 2003, but the CNMI has been relatively wet.  While the rainfall during May-July 2003 could still fall a bit below normal, no major impacts of dry weather (wildfires, desiccation of grasslands, and problematic draw down of surface water supplies) are anticipated.  The threat of typhoons for Guam and the CNMI should be normal during 2003.  Approximately four tropical cyclones should brush past Guam and Saipan within 200 miles, but a direct hit by an intense typhoon is unlikely.

    Predicted rainfall for the Mariana Islands from May 2003 through April 2004 is as follows:
 
 
Inclusive Period
% of Long-Term Average
---
      Guam/Rota                                              Saipan/Tinian
    May 2003 - Jul 2003
           85%                                                          85%
Aug 2003 - Oct 2003
           95%                                                          95%
 Nov 2003- Apr 2004 
           90%                                                          90%
source: UOG-WERI

Yap State: Stations on the main island of Yap and on the atolls of Yap State all began to experience persistent dryness from November 2002 through February 2003.  Then, many stations were wetter than normal in March.  The Weather Service Office near the Yap Airport recorded 5.98 inches (82%) in January, 1.69 inches (28%) in February, and 7.63 inches (128%) in March, or 79% of normal rainfall for the three months.  Rainfall amounts on Ulithi were 2.50 inches (40%) in January, 1.02 inches (20%) in February, and 6.36 inches (125%) in March, or 60% for the 3-month period.  Farther south at Woleai Atoll (which is normally wetter than Yap and Ulithi year-round), persistent dryness has occurred from October 2002 through March 2003.  The rainfall was 3.90 inches (37%) in January, 4.60 inches (61%) in February, and 1.35 inches (16%) in March, for a 3-month average of 37%.

   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 following year. The persistent dryness that set in late in the El Niño year 2002 continued at most Yap stations through at least February 2003.  Wet weather returned to many locations in March.  While the rainfall during May-July 2003 could still fall a bit below normal, no major impacts of dry weather (wildfires, desiccation of grasslands, and problematic draw down of surface water supplies) are anticipated.  Super Typhoon Kujira passed well to the north of Yap in mid-April.  The tropical cyclone threat at Yap should be normal in 2003.

   Predicted rainfall for Yap State from March 2003 through April 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
May 2003 - Jun 2003
  80% 
Jul 2003 - Oct 2003
   100% 
Nov 2003 - Apr 2004
    95% 
source: UOG-WERI

Chuuk State:  Rainfall at islands and atolls in the southern part of Chuuk State has been heavier and more frequent than expected.  However, some of the atolls in the north experienced a prolonged modest reduction of rainfall that began in October 2002 and persisted through March 2003.  A moderate and persistent reduction of rainfall may still occur in the northern portions of Chuuk State until July, after which the rainfall at all locations in Chuuk State is expected to return to near normal.  During January, February, and March, the Weather Service Office at Weno Island measured 10.06 inches (94%), 4.72 inches (76%), and 7.95 inches (95%).  This amounted to 90% of normal rainfall for the 3-month period.  At Lukunoch, rainfall for January, February, and March was 5.60 inches (52%), 5.06 inches (82%), and 8.79 inches (105%) for the respective months.  This amounted to 77% of normal for the 3-month period.  At Polowat in the western atolls, it was slighlty drier than at Weno.  The rainfall for January, February, and March at Polowat was 6.36 inches (80%), 5.86 inches (94%), and 4.15 inches (66%), or 80% of normal for the 3-month period.

   Two tropical cyclones affected Chuuk State in the first four months of 2003:  the tropical disturbance that became Tropical Storm Yanyan in January, and Typhoon Kujira in April.  Yanyan was only a tropical disturbance when it passed through Chuuk State and provided some beneficial rains.  Typhoon Kujira passed to the north and did not have any major impacts.  The threat from tropical cyclones for Chuuk State in 2003 should be near normal.

    Predictions for Chuuk State from May 2003 through April 2004 are as follows:
 
Inclusive Period
% of Long-Term Average
May 2003 - Jun 2003
  85% 
Jul 2003 - Oct 2003
  95% 
Nov 2003 - Apr 2004
   90% 
source: UOG-WERI

Pohnpei State:  Rainfall at Pohnpei State has been heavier and more frequent than expected.  Thus, expected moderate drought conditions did not materialize with this current ENSO event.  With the notable exception of Kapingamarangi, the islands and atolls of Pohnpei State experienced slightly drier than normal conditions during most of the months from October 2002 through March 2003.  At the Weather Service Office at Kolonia, the January, February, and March rainfall totals were 10.71 inches (82%), 7.90 inches (73%), and 16.25 inches (120%), respectively.  This amounted to a 3-month total of 34.86 inches or 93% of average precipitation.  At Pingelap, observed rainfall in January, February, and March was 18.52 inches (150%), 6.68 inches (55%), and 8.06 inches (56%), respectively, for a 3-month amount of 85%.  At Nukuoro, January through March precipitation amounts were 4.47 inches (38%), 6.07 inches (58%), and 18.89 inches (139%), respectively, for a 3-month amount of 82%.  Kapingamarangi picked up a substantial amount of rain during January through March with totals of 14.57 inches (101%), 14.80 inches (144%), and 14.87 inches (107%) for the three months.  Convection along the equator and enhanced monsoonal westerlies have kept Kapingamarangi in rainfall surpluses for almost every month since April 2001.  During the first quarter of 2003 the highest measured rainfall total at any station in Pohnpei State (and at any recording station in all of Micronesia) was the 44.24 inches measured at Kapingamarangi.

   Tropical cyclones and several tropical disturbances that later became named tropical cyclones affected Pohnpei State through most of 2002 and again in January 2003 when an area of disturbed weather associated with the developing Tropical Storm Yanyan affected portions of Pohnpei State.  Further, in April 2003 the developing Super Typhoon Kujira passed close to Pohnpei and caused very heavy rainfall (when still a tropical storm).  Flooding in Kolonia from heavy rains was reported by residents to have been the worst in 60 years.  A young man died when high winds toppled a tree onto him, and a few days before the passage of the cyclone, a boat capsized in rough seas resulting in a drowning death.  Despite an early start to tropical cyclone activity in Pohnpei, the threat of tropical cyclones should be normal for the rest of 2003.

   Predicted rainfall for Pohnpei State from May 2003 through April 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
--- 
Pohnpei Islands and Atolls            Kapingamarangi
May 2003 - Jun 2003
             85%                                     80%
Jul 2003 - Sep 2003
             95%                                     80%
Oct 2003 - Apr 2004
             90%                                     75%
source: UOG-WERI

Kosrae State:  Rainfall stations on Kosrae experienced a small decrease in rainfall totals during the first quarter of 2003, but expected moderate drought conditions did not materialize with this current ENSO event.  Rainfall at Kosrae (SAWRS) during January, February, and March was 17.78 inches (123%), 9.33 inches (57%), and 15.13 inches (81%) respectively.  The 3-month total of 42.24 inches was 85% of the normal total of 49.41 inches.  The three other Kosrae stations (Tofol, Tafunsak, and Utwa) were drier than SAWRS, with 3-month totals of 37.69 inches (76%), 33.37 inches (68%), and 33.62 inches (68%), respectively.

   Rainfall for Kosrae State is expected to be near normal for the remainder of 2003 with the possibility of some limited periods of dry weather through July that will not be extensive enough to cause any problems.  The threat posed by tropical cyclones to Kosrae will be normal during 2003.

   Predicted rainfall for Kosrae State from May 2003 through April 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
May 2003 - Jul 2003
80%
Aug 2003 - Oct 2003
95%
Nov 2003 - Apr 2004
90%
source: UOG-WERI

Republic of Palau: Conditions at Palau (which were drier than normal at most locations for most of the second half of 2002), were wetter than anticipated during the first quarter of 2003.  Rainfall at the Weather Service Office at Koror during January, February and March was 8.88 inches (83%), 13.48 inches (148%), and 7.65 inches (93%), respectively.  The 3-month average was 107% of normal.  The monthly rainfall distribution at Nekken Forestry was slightly wetter overall than at the Weather Service Office in Koror with 10.40 inches (97%) in January, 10.67 inches (117%) in February, and 10.68 inches (130%) in March.  Farther south at Peleliu, it was drier, and rainfall totals for January-March were 7.18 inches (67%), 10.10 inches (112%), and 7.19 inches (88%) respectively.

   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, the first half of 2002 was generally drier than normal.  But dry conditions did not persist into 2003.  Rainfall for Palau is expected to be near normal for the remainder of 2003 with the possibility of some limited periods of dry weather through July that will not be extensive enough to cause any problems.

   Two tropical cyclones formed in Micronesia in the first three months of 2003, and passed well to the northeast of Palau:  Tropical Storm Yanyan in January and Super Typhoon Kujira in April.  Neither of these tropical cyclones had any major effect on Palau.  The threat from tropical cyclones will be normal for 2003.

   Predicted rainfall for Palau from May 2003 through April 2004 is as follows:
 
Inclusive Period
% of Long-Term Average
May 2003 - Jul 2003
80%
Aug 2003 - Nov 2003
95% 
Dec 2003 - Apr 2004
90% 
source: UOG-WERI

Republic of the Marshall Islands (RMI):  Although some of the atolls of the RMI have been quite dry (especially in the north), many islands have received adequate rainfall.  After abundant rainfall during most of 2002 in the central and southern RMI, the first quarter of 2003 was near normal.  Only in northern atolls, such as Kwajalein, Wotje, and Utirik did dry conditions set in late in 2002, and continue into 2003.  The Majuro weather station measured 8.62 inches (102%), 9.95 inches (162%), and 1.47 inches (18%) during January, February and March.  The very low March total at the Majuro WSO may be an incomplete record. The March total for Laura on the west side of Majuro Atoll was similar at 1.66 inches (20%).  For the 3-month period, the average for Majuro was 88% of normal.  Rainfall at Kwajalein (and nearby Ebeye) was 2.75 inches (60%) in January, 2.36 inches (73%) in February, and 2.08 inches (51%) in March, for a three month average of 60%.  Other atolls in the northern part of the RMI such as Wotje and Jaluit reported very dry totals of 8.55 inches (37%) and 2.79 inches (25%) for the first quarter of 2003.

   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 are one of the few regions in Micronesia where some extended periods of dry weather are expected.  Still, they will not be extensive enough to cause serious drought conditions before seasonal rains return. Continued conservation measures may still be needed for the northern Marshall Islands into June.

   During 2002, tropical cyclone activity shifted east of normal in the western North Pacific basin, and westerly winds pushed as far east as the central and southern Marshall Islands.  Many tropical disturbances moved through the RMI, some of which later moved west and became named tropical cyclones.  During 2003, the monsoon trough should return to its normal location, easterly winds should prevail in the Marshall Islands, and the tropical cyclone threat for the RMI should be low.

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



APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 17 April 2003, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY:  issued by Climate Prediction Center/NCEP on April  10, 2003

    Warm episode (El Niño) conditions continued to weaken during March 2003, as the equatorial easterlies strengthened and SST anomalies decreased throughout the eastern and central equatorial Pacific. Since December, SST anomalies have decreased by more than 2°C in the eastern equatorial Pacific between 130°W and the South American coast. This decrease has resulted in near normal or slightly below normal SSTs in the region east of 120°W since February. During the same period there has also been a steady decrease in the magnitude and extent of the positive subsurface temperature anomalies, indicating a depletion of the excess warmth in the upper ocean of the equatorial Pacific. This evolution is typical during the decay phases of warm episodes.

   In spite of these trends, significant positive SST anomalies remained in the central equatorial Pacific during March 2003, with anomalies greater than +1°C extending from 170°E to 140°W. Greater-than-average precipitation and cloudiness were found over the western portion of this region, although the departures from average and the spatial coverage have decreased substantially during the last two months. The Tahiti-Darwin SOI remained negative (-1.0) for the 13th consecutive month, while the equatorial SOI was near zero.

   A comparison of the 2002-03 El Niño episode with previous events in the last 50 years indicates that for the equatorial Pacific as a whole the 2002-2003 event was moderate in intensity. The SST departures associated with the event were greatest in the central equatorial Pacific (Niño 4 and Niño 3.4 regions) and least in the eastern equatorial Pacific (e.g., Niño 3 and especially Niño 1+2).  This pattern of anomalous warming, combined with the rapid weakening of the event, had a generally weaker than expected influence on the atmospheric circulation and hence the precipitation and temperature patterns over North and South America during January - March 2003.

   Consistent with current conditions and recent observed trends, a majority of the coupled model and statistical model forecasts indicate that near-normal conditions will prevail through September 2003. However, there is uncertainty in this forecast as some forecasts indicate the possibility of continued weak El Niño conditions while others indicate the development of La Niña conditions during the second half of 2003.
 

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 (June - August 2003 and September - November 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: 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.
 

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