Pacific ENSO Update

3rd Quarter 2001 - Vol. 7 No. 3


CURRENT CONDITIONS


Sea surface temperatures (SSTs) across the tropical Pacific are near normal, with a distribution of slightly warmer than normal SST in the Western and Central equatorial Pacific, and slightly cooler than normal SST in the Eastern equatorial Pacific. The Southern Oscillation Index (SOI) has fallen to weak negative values for the last few months after being positive for almost three years. Persistent and strong low-level easterly wind anomalies in equatorial latitudes of the Western and Central equatorial Pacific have weakened in recent months. The SST distribution in the tropical Pacific, the status of the SOI, and the weakening of the low-level easterly winds are indicative of a climate state that is neither El Niņo nor La Niņa (designated by some as "El Niņo-neutral"). Over the past two years there has been a gradual eastward expansion of the area of positive subsurface temperature anomalies into the central Pacific supporting the current demise of the long-lived La Niņa and perhaps signaling the imminent start of the next warm episode. Some climate prediction models are indicating the beginning of a weak or moderate El Niņo late in 2001 or early 2002.

Rainfall amounts at most islands were drier than normal during the first half of 2001 (Figure 1) with notable exceptions in the area of the Republic of Palau and at Kapingamarangi. Contributing to high rainfall on Palau were several tropical disturbances and some near passages of developing tropical cyclones that formed in the Philippine Sea. At Kapingamarangi, warming SSTs and a return of near-normal low-level wind (including a few episodes of westerly wind) accompanied a return of episodes of heavy shower activity at its near-equatorial location in the western North Pacific. The Marshall Islands and the CNMI were exceedingly dry. Of all the Mariana Islands, only parts of Guam returned to near normal rainfall in the period April-June, the result of several episodes of intense daytime island thunderstorms during June. During July, normal monsoonal wind episodes in Micronesia and the occurrence of several tropical disturbances that became tropical cyclones in the Philippine Sea, caused enhanced rainfall in the Republic of Palau, Yap State, and Guam. Island groups of the eastern Carolines and Marshall Islands saw near or below normal rainfall in July.

SST

Sea surface temperatures (SSTs) across the tropical Pacific are near normal, with a distribution of slightly warmer than normal SSTs in the Western and Central equatorial Pacific, and slightly cooler that normal SSTs in the Eastern equatorial Pacific. Persistent warmer than normal SST anomalies in the equatorial central Pacific and much of the equatorial Western Pacific have gradually increased, and in the NINO 4 region (5°N-5°S, 160°E-150°W), July's value of +0.5ēC is the warmest it has been there since March 1998. SST values remain below normal in the Eastern equatorial Pacific east of about 120°W. The general consensus of international Global Climate Models (GCMs) is still for some Pacific warming in the coming months. In fact, of 11 climate models, 6 are predicting neutral conditions through 2001, three are predicting warm conditions of 1ēC or less by January 2002, and two are indicating El Niņo by spring 2002. Definitions of El Niņo developed in the early 1980s were contingent on persistent SST anomalies of at least +1ēC along the tropical Pacific coast of South America, while more recent definitions have focused on persistent SST anomalies of at least +0.4ēC in the Central equatorial Pacific. At this time, it is too early to accurately predict when Central Pacific SST anomalies - along with other climate indicators -- will become large enough for sufficient time to declare the next El Niņo event, but based on current SST distribution, slightly negative values of the SOI, near-normal equatorial Pacific winds, and a near-normal distribution of tropical cyclones, it does not seem likely that this will occur until late 2001 or early 2002.

The depth of the equatorial oceanic thermocline (as represented by the depth of the 20°C isotherm) continued to remain deeper than normal in the Western Pacific and near normal in the extreme Eastern Pacific. Over the past two years there has been a gradual eastward expansion of the area of positive subsurface sea temperature anomalies into the central Pacific supporting the current demise of the long-lived La Niņa. As recently as March 2001, colder than normal sub-surface temperatures in the Central and Eastern equatorial Pacific were -4°C and -2°C respectively. Since then, the Central Pacific subsurface temperatures have warmed to as much as 2°C above normal at depths of 100 meters, while the subsurface temperatures in the far eastern part of the equatorial Pacific have remained somewhat colder than normal. The gradual eastward expansion of warmer than normal sub surface water is yet another indicator of a possible start of the next El Niņo in late 2001 or early 2002.

SOI

During April through June 2001, SOI values were slightly negative (-0.1, -0.8, -0.1 respectively), indicating the demise of a prolonged period of weak to moderate La Niņa conditions. The July value of the SOI was -0.4. Consistent with the SOI falling from positive values in the winter of 2001 to weak negative values in the spring and early summer, the easterly wind flow of the equatorial Pacific weakened and the monsoon trough pushed out to near normal locations in Micronesia by late June and July. The trade wind trough across eastern Micronesia was weaker than it was during the past two years, especially in the Marshall Islands. As a result, the long east-west band of persistently heavier than normal rainfall characteristic of the 1999 and 2000 La Niņa events was much shorter in length and narrower in breadth during the first half of 2001. Cloudiness and showers associated with the South Pacific Convergence Zone (SPCZ) have been focused a bit southwestward of normal, leaving American Samoa in dry trade wind flow for much of the past few months.

Over the period April to June 2001, easterly low-level winds dominated the low latitudes (5ēN-5ēS) of the tropical Pacific with a few episodes of low-level westerly winds extending to near 150°E. The strength of these easterly winds, however, dropped to near normal velocity after being as much as 10 knots stronger than normal for much of 1998 to early 2001. In the upper troposphere (30,000-50,000 ft), winds over Micronesia were near normal, and so also were the patterns of rising and sinking air. The normal downward (sinking air) branch of the large-scale tropical atmosphere along the equator in the eastern equatorial Pacific did not extend as far west as in the previous two years, so rainfall on islands near the equator in the western North Pacific (such Kapingamarangi) experienced increased rainfall. We expect the SOI to remain slightly negative (El Niņo-neutral values) through the fall, then to trend towards values nearer -1.0 by early 2002. With the SOI in weak negative territory, atmospheric circulation patterns should exhibit more normal behavior. The positions (and natural fluctuations) of the monsoon troughs, the trade wind troughs (ITCZs), the South Pacific Convergence Zone (SPCZ), and the mid-latitude jet streams should become more normal, with fairly standard distributions of clouds and rainfall. It should be understood that "normal behavior" characteristically exhibits high month-to-month variability in the cloudiness and rainfall.

TROPICAL CYCLONE ACTIVITY

Western North Pacific tropical cyclone activity through July 15, 2001 was near normal with five tropical cyclones - Cimaron, Chebi, Durian, Utor, and Trami -- named by the Japan Meteorological Agency (JMA). The Joint Typhoon Warning Center (JTWC) identified 8 total tropical cyclones including three tropical depressions in addition to those named by the JMA. Most of the western North Pacific tropical cyclones developed in western longitudes - forming near Guam, but becoming tropical storms or typhoons after moving into the Philippine Sea. Tropical cyclone activity from July 2000-June 2001 in the Southern Hemisphere was characterized by much lower than normal activity (21 numbered by the JTWC versus a normal of 28). Based on the expected slightly warmer than normal SST in the western North Pacific and weakly negative SOI by the boreal summer, normal tropical cyclone activity in the western North Pacific is anticipated for the second half of 2001. This means that much of Micronesia should be affected by tropical cyclone activity from September until late-December. In eastern Micronesia, this activity should be limited to a few developing tropical storms and a possible typhoon in the Marshall Islands, especially late in the fall, and to the fringe effects of storms passing to the north for Pohnpei State and Kosrae State. American Samoa is not expected to experience a significant tropical cyclone until the next El Niņo event, although the region could see a tropical depression or weak tropical storm in the January-April 2002 timeframe.


NOAA's Climate Prediction Center in Washington D.C. routinely monitors the latest forecast results from several ENSO models. THE PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS outlines the these results.


LOCAL VARIABILITY SUMMARIES:

State of Hawaii: Anomalous weather patterns served as "bookends" for July. During the first 5 days of the month, the low level subtropical ridge was pushed unusually close to the Hawaiian Islands with the net result being local land and sea breezes instead of the usual trade winds. Conditions were also very stable and most daily rainfall totals were less than 0.10 inches.

The resumption of moderate to fresh trades occurred on 6 July and persisted through 28 July. Rainfall activity within this more typical summer weather pattern was mainly over the windward areas of the state.

July 2001 ended with 3 days of unusually strong trade winds more reminiscent of early spring. Accompanying these strong trades were the shower areas associated with the remnants of Tropical Storm Erick, an eastern Pacific tropical cyclone that dissipated near 21N 129W on 23 July. While frequent showers were the rule, the strong trades kept these showers moving along without producing any flooding problems.

Kevin Kodama - Senior Service Hydrologist, NWSFO Honolulu, HI

For a more complete summary, and the county by county wrap-ups, please see the July 2001 Precipication Summary from the National Weather Service Honolulu Weather Forecast Office.

American Samoa: Rainfall at the Pago Pago Airport for April, May, and June was 6.62 inches (55%), 4.79 inches (48%), and 4.61 inches (62%), respectively, amounting to 55% of normal for the 3-month period. The very dry conditions in the Samoa region for the April-June period were due to persistent dry trade wind flow. Cloudiness and showers associated with the South Pacific Convergence Zone (SPCZ) have been focused a bit southwestward of normal, leaving American Samoa in dry trade wind flow for much of the past few months.

With equatorial SST anomalies and the SOI expected to be near normal through the fall of 2001, the rainfall from July 2001 through the end of the forecast period should average near normal. During the past three years of persistent La Niņa (the last half of 1998 to early 2001 -- years fairly similar in terms of SST and SOI values), the rainfall in American Samoa was near normal to slightly wetter than normal. Rainfall in American Samoa is not as closely tied to ENSO as it is in other regions. While some of the very dry periods (1982-83*, 1987*, 1990, 1993, and 1998*) at American Samoa have occurred in association with major El Niņo events (years shown with a "*"), and some of the very wet periods (1980-81*, 1985-86*, 1994, and 1999) have occurred in years prior to major El Niņo events (years shown with a "*"), there is not a consistent ENSO signal in the rainfall there on average. While it is too early to predict the next El Niņo, it does not appear that a significant event will occur before 2002, such an event should not affect rainfall in American Samoa during this forecast period.

Significant tropical cyclone activity is not expected in the Samoa region until after the next El Niņo event occurs. Despite this, some tropical depressions and weak tropical storms could develop in the portion of the SPCZ that connects to the eastern reaches of the Australian northwest monsoon trough during the November 2001-April 2002 timeframe, bringing heavy rains to the Samoan Islands as the cyclones move through the region.

Predicted rainfall for American Samoa from August 2001 through September 2002 is as follows:


Inclusive Period         % of long-term average
                              Samoa Region
Aug 2001 - Sep 2002             90% - 95%

- sources: UOG-WERI and PEAC

Guam/CNMI: Rainfall at the Guam International Airport (GIA) during April, May, and June was 1.15 inches (29%), 2.27 inches (38%), and 13.12 inches (203%), respectively. This amounted to 101% of the normal value for the period April-June. Andersen Air Force Base (AAFB) measured 2.28 inches (47%), 3.02 inches (46%), and 6.74 inches (106%), or 67% of the average rainfall for the period. Long spells of nearly cloudless, hot, dry weather in April and May, gave way to fortuitous development of day-time island thunderstorms during June that produced a near-record June rainfall at the airport, but varied greatly around the island, with some locations reporting June rainfall totals of less than half of the airport total, or approximately 6 inches. July rainfall on Guam was nearly 15 inches at most locations (partly the result of the near passage of the tropical disturbances that became tropical cyclones Utor, Kongrey, Yutu, and Toraji), and thus, the deleterious effects of a dry winter and spring (e.g., wildfires; low water levels in scenic streams, popular waterfalls, and swimming holes; and low water level in the Fena Reservoir) abated.

April, May, and June rainfall at Saipan International Airport (SIA) was 0.80 inches (29%), 2.04 inches (46%), and 3.53 inches (76%), or 54% of the average for the period. For April, May, and June, Capitol Hill's measured rainfall was 1.82 inches (52%), 3.32 inches (60%), and 6.41 inches (111%). Thus, at Capitol Hill, quarterly rainfall was somewhat higher at 78%. The helpful thunderstorm activity on Guam during June, did not affect Saipan, Tinian and Rota as much, and dry conditions continued their grip. Rainfall amounts for the 3-month period at the Tinian Airport were 1.47 inches (42%), 3.00 inches (55%), and 5.04 inch (87%), respectively. The 3-month rainfall for Tinian Airport was below normal at 64%. At Rota Airport, April, May, and June rain amounts were 2.53 inches (56%), 3.02 inches (48%), and 4.20 inches (68%). This gave a 3-month average of only 57%. On the northern part of Rota, at the beautiful Rota Resort and Country Club, the NASA TRMM network there recorded 141% of the amount at the Rota Airport for the period April-June. Very dry conditions prevailed on the CNMI during the winter and spring of 2001, and only on Guam was their significant relief in June due to intense island thunderstorms.

Based on 30 years of rainfall data, non-ENSO years on Guam and the CNMI tend to be slightly wetter than the average. This should be expected since monsoon and tropical cyclone activity are normally greater during these years. Thus "El Niņo neutral" rainfall for the Mariana Islands is somewhat greater than the long-term average or 105-110% above the long-term average. As is common during "normal" periods, there can be high month-to-month variability in the rainfall. While it is too early to predict the next El Niņo, an event in 2002 would likely not significantly affect Guam and the CNMI during this forecast period. During the second half of 2001, tropical cyclone activity should return to normal after three years of well-below normal activity. Thus, the Mariana Islands can expect typhoon threats from August through December, with October and November being the months of greatest threats. Most of these will approach from the east-southeast.

Predicted rainfall for the Mariana Islands from August 2001 through September 2002 is as follows:


Inclusive Period         % of long-term average
                      Guam/Rota       Saipan/Tinian
Aug 2001 - Sep 2002     110%              110%

- sources: UOG-WERI

Yap State: Abundant rain returned to the Northern Yap State for the three months of April, May, and June, after being quite dry there during the previous quarter. The weather station at the Yap Airport recorded 2.30 inches (40%) in April, 10.80 inches (119%) in May, and 15.13 inches (119%) in June, or 103% of normal rainfall for the three months. This was a bit wetter (especially for the months of May and June) than the 94% experienced during the previous quarter. April, May, and June rainfall amounts on Ulithi were 5.35 inches (109%), 7.56 inches (98%), and 12.41 inches (115%) or 108% for the 3-month period. This was much wetter than the 74% of the previous quarter. Farther south at Woleai Atoll, rainfall was 8.90 inches (81%) in April, 12.81 inches (105%) in May, and 13.75 inches (106%) in June, for a near normal 3-month average of 98%.

Rainfall for Yap State is expected to be about 100%-110% of the long-term average, depending on location. When all ENSO events in the last 30 years are considered, the wetter than normal La Niņa conditions do not quite add up to the deficits caused during El Niņo-induced droughts. Thus, "normal, or non-ENSO year" rainfall for Yap State must make up for this deficit, and thus should be greater than 100% of the long-term average. This additional rain is due to increased monsoon activity and to increased tropical cyclone occurrence. Tropical cyclone activity should be normal, and this means that the northern Yap State islands could be affected by tropical storms and typhoons from September through mid-December, while southern islands can be affected from mid-October until late-December.

Predicted rainfall for Yap State from August 2001 through September 2002 is as follows:


Inclusive Period                % of long-term average
                             Yap               Outer Atolls:
                            Island       S.of 8·N     N. of 8·N
Aug 2001 - Oct 2001          110%          100%         110%
Nov 2001 - Sep 2002          110%          115%         110%

- sources: UOG-WERI

Chuuk State: During April, May, and June, the weather station at Weno Island measured 6.31 inches (51%), 9.71 inches (79%), and 9.80 inches (84%). This amounted to only 71% of normal amounts for the 3-month period. This was quite a change from the previous three months when Weno was very wet with 145% of normal rainfall. Chuuk State islands to the north and south were a bit wetter overall. In the Mortlocks at Lukunoch, rainfall for April, May, and June was 14.33 inches (116%), 9.10 inches (74%), and 10.07 inches (86%) for the respective months. The 3-month average was 92%. Rain for Polowat in April, May, and June was 6.74 inches (112%), 9.99 inches (111%), and 6.13 inches (49%) in the respective months, giving a net below-normal 3-month average of 83%. Although quite variable from month-to-month, the overall dryness in Chuuk State during April through June reflected a decrease in the shower and thunderstorm activity along the tradewind trough, and a lack of early season tropical cyclone development.

Rainfall for all of Chuuk State is expected to be slightly wetter than normal, but with high month-to-month variability. Over the last 30 years, the El Niņo-induced droughts have led to much larger rainfall deficits than the La Niņa-associated rainfall excesses. Thus, normal years and years leading into another El Niņo should be wetter to make up for the El Niņo-related rainfall deficit. This is due to increased monsoon activity and to some extent on increased tropical cyclone activity. Tropical cyclone activity should return to normal in Chuuk State for the second half of 2001. This means that several tropical disturbances will move over Chuuk that later move northwest and become tropical cyclones. Chuuk will also have a higher risk of getting a tropical storm or typhoon, primarily during the months of October, November, and December.

Predictions for Chuuk State from August 2001 through September 2002 are as follows:


Inclusive Period               % of long-term average
                        Chuuk         Outer Atolls
                        Lagoon    Southern    Western
Aug 2001 - Oct 2001     100%       100%        100%
Nov 2001 - Sep 2002     110%       115%        110%

- sources: UOG-WERI

Pohnpei State: As in Chuuk State, rainfall in Pohnpei State was generally drier than normal for the three-month period April-June. Also similar to Chuuk State, the dryness of April, May and June followed generally very wet conditions in January, February and March. At the weather station at Kolonia, the April, May, and June rainfall totals were 12.17 inches 74%), 11.17 inches (58%), and 14.83 inches (87%), respectively. This amounted to a 3-month value of 72% of average precipitation. At Pingalap, observed rainfall in April, May, and June was 7.27 inches (42%), 8.66 inches (51%), and 10.77 inches (66%), respectively, for a 3-month amount of 66%. At Nukuoro, April through June precipitation amounts were 13.55 inches (90%), 15.82 inches (107%), and 10.58 inches (87%), respectively. Further south, Kapingamarangi saw a large increase in rainfall. April, May and June measurements there were 14.33 inches (53%), 14.85 inches (144%), and 16.93 inches (234%), respectively, giving a 3-month average of 148%. This made Kapingamarangi the wettest location with rainfall measurements in Micronesia in terms of percent of rainfall (Figure 1).

Over the last 30 years, the El Niņo-induced droughts have led to much larger rainfall deficits than the La Niņa-associated rainfall excesses. Thus, normal years and years leading into another El Niņo should be wetter to make up for the El Niņo-related deficit. As a result, rainfall for all areas of Pohnpei State is expected to be near normal through October, then somewhat above normal for the remainder of the forecast period. At all locations, high month-to-month variability in rainfall can be expected. While it is too early to predict the next El Niņo, an event in 2002 would likely produce heavier than normal rainfall for Pohnpei State during the winter of 2001-2002 and the spring of 2002. October 2001-March 2002 rainfall predictions reflect this possibility. Even though tropical cyclones are not expected to pose a serious threat to Pohnpei State until the next El Niņo event, the islands could experience some periods of high waves and heavy rains with strong westerly winds from typhoons passing to the north. [NOTE: Pohnpei State will likely have greater TC threats in the spring of 2002 if the equatorial westerlies develop.]

Predicted rainfall for Pohnpei State from August 2001 through September 2002 is as follows:


Inclusive Period          % of long-term average
                     Pohnpei           Outer Atolls:
                     Island    Eastern    Southern    Equatorial
Aug 2001 - Oct 2001   100%      110%        100%        110%
Nov 2001 - Sep 2002   110%      115%        120%        130%

- sources: UOG-WERI

Kosrae: Kosrae was dryer than normal, with the April total of 9.74 inches being only 44% of normal. The June total of 17.14 inches at Kosrae recovered to within 90% of normal. The dryness of Kosrae during April to June was in stark contrast to the very high amounts of rainfall there during January to March when Kosrae was the wettest location in Micronesia in terms of percent of rainfall. This dryness resulted from a weakening of the persistent trade wind trough that was anchored in the area earlier in the year. Utwa and Tafunsak were also dryer than normal with 39% and 66% respectively for the three months, while Tofol was close to normal with 90%.

Over the last 30 years, the El Niņo-induced droughts have led to larger rainfall deficits than the La Niņa-associated rainfall excesses, although Kosrae's La Niņa-induced springtime rainfall is the largest measured in Micronesia. Thus, normal years and years leading into another El Niņo should be wetter to make up for the El Niņo-related deficit. Rainfall for Kosrae is expected to be near normal from August through October, and above normal for the remainder of the forecast period. However, high variability should be expected in the month-to-month rainfall amounts. While it is too early to predict the next El Niņo, an event in 2002 would likely produce heavier than normal rainfall for Kosrae State during the winter of 2001-2002 and the spring of 2002. Nov 2001-Mar 2002 rainfall predictions reflect this possibility. Kosrae could experience a rare tropical cyclones when the next El Niņo event begins.

Predicted rainfall for Kosrae State from August 2001 through September 2002 is as follows:


Inclusive Period     % of long-term average
Aug 2001 - Oct 2001            100%
Nov 2001 - Sep 2002            115%

- sources: UOG-WERI

Republic of Palau: Rainfall at Koror during April, May, and June was 13.27 inches (153%), 13.86 inches (116%), and 22.53 inches (130%), respectively. The 3-month average was 130% of normal compared with 92% for the previous quarter. In July, there was continued abundant rainfall of 21.77 inches (121%). For the 3-months of April, May, and June, rainfall at the Mariculture Center was roughly the same as that at the Weather Station and rainfall at Nekken Forestry was 23% more than that at the Weather Station. Farther south at Peleliu, conditions were drier with 11.80 inches (131%) in April, 9.94 inches (83%) in May, and 13.70 inches (81%) in June. This produced a 3-month average of 93%. The passage near Palau of several tropical disturbances (some of which became numbered or named tropical cyclones) helped to produce copious rainfall at the more northern locations.

Over the last 30 years, the El Niņo-induced droughts and the La Niņa-associated rainfall excesses have nearly cancelled each other. Thus, normal years and years leading into another El Niņo should be near average to slightly wetter than average. For the entire Palau island chain, we expect rainfall to be wetter than normal for the rest of 2001. Characteristic of "normal" conditions is the likelihood of high month-to-month variability in rainfall. This rainfall behavior should last until the next El Niņo event begins. Tropical cyclone activity should also return to normal, meaning that all islands from Angaur northward could experience a tropical cyclone from October through December. Islands south of Angaur are generally not directly threatened by typhoons, although typhoons passing to the north could cause dangerous surf and heavy rainsqualls with gusty southwesterly wind.

Predicted rainfall for Palau from August 2001 through September 2002 is as follows:


Inclusive Period              % of long-term average
                    Koror and           Outer Atolls
                    Mountain Is.  S. of 8ºN    N. of 8ºN
Aug 2001 - Oct 2001   100%            100%        100%
Nov 2001 - Sep 2002   105%            105%        110%

- sources: UOG-WERI

Republic of the Marshall Islands (RMI): Quite dry conditions dominated the Republic of the Marshall Islands (RMI) during the first half of 2001. The trade wind trough that often occurs in the spring across the RMI during La Niņa events only occurred sporadically. Generally, it was more persistent to the west. During April, May, and June, the Majuro weather station (representative of the southern islands) measured 4.07 inches (40%), 7.07 inches (69%), and 15.10 inches (130%). For the 3-month period, the average for Majuro was 79% (thanks to abundant rain in June). For April, May, and June net rainfall amounts at nearby Laura (77%) averaged close to those at Majuro weather station. In July, Majuro recorded below normal rainfall with 10.04 inches, or 77% of normal. Kwajalein rainfall (representative of the central islands) was very dry during the first three months of 2001 and again during April, May and June. Rainfall at Kwajalein (and nearby Ebeye) was 2.17 inches (29%) in April, 4.68 inches (47%) in May, and 4.63 inches (48%) in June. This was an average of only 42% for the period. In July, rainfall increased to 7.73 inches, but this was still below normal (74%) for the month.

Ailingalaplap continued to be drier than normal. Even Jaluit, which was very wet during the last few months of 2000, became significantly drier than normal. During April, May, and during July, Jaluit had 6.10 inches (59%), 9.96 inches (89%), and 7.09 inches (56%), respectively. Farther north, Wotje continued to be the driest of the locations that measured rainfall during the year. In the January-March timeframe, rainfall amounted to a 3-month amount of only 3.63 inches (30%). And during April, May, and during July, the accumulated rainfall there was an extremely low value of 5.32 inches (14%). Observations were not available from Utirik during January through April; however, satellite imagery indicated that it was also likely very dry. May rainfall there was 4.85 inches (57%) and during July it was only 1.57 inches (18%). The values of rainfall in the northern islands of the RMI seem very low, but are supported by satellite imagery showing most of the rainfall confined to showers along the trade wind trough which tended to be south of these islands.

The Tropical Upper Tropospheric Trough (TUTT) became well established in the western North Pacific during July, and should act to bring a return of near normal rainfall to the RMI for the remainder of the summer of 2001. Thus, rainfall for the Marshall Islands is expected to be near the long-term average through October and then above the long-term average for the remainder of the forecast period. While it is too early to predict the next El Niņo, an event in 2002 would likely produce heavier than normal rainfall for the south and central Marshall Islands during the winter of 2001-2002 and the spring of 2002. May 2001-Jun 2002 rainfall predictions reflect this possibility. Tropical cyclone activity for the Marshalls should return to normal, meaning that Wake and Enewetok could experience a typhoon from September into November. The remainder of the islands south of 12 °N could experience a tropical storm or minimal typhoon in October and November. The eastern Marshall Islands will not likely experience an intense typhoon until the fall of the next El Niņo year (not expected until 2002 or later).

Predicted rainfall for the RMI from August 2001 through September 2002 is as follows:


Inclusive Period           % of long-term average
                                  RMI Atolls
                            Southern     Central   Northern 
Aug 2001 - Oct 2001           100%         100%       90%
Nov 2001 - Sep 2002           110%         120%      130%

- sources: UOG-WERI


APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 16 August 2001, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY

SPECIAL SECTION - Markov model for Pacific SST and sea level

SPECIAL SECTION - Experimental Forecasts for Pacific Island Rainfall


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 PREDICTION 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 - Manoa Campus
HIG #225, 2525 Correa Road, Honolulu, Hawaii 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 INSTITUTE (WERI):
Lower campus, University of Guam
UOG Station, Mangilao, Guam 96923
Contact C. Guard or M. Lander at (671)735-2685 for more info on tropical cyclones and climate in the Pacific Islands.

University of Hawaii (UH) School of Ocean and Earth Science and Technology
(SOEST) DEPARTMENT OF METEOROLOGY:
HIG #350, 2525 Correa Road, Honolulu, Hawaii 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:
HIG #350, 2525 Correa Road, Honolulu, Hawaii 96822
Contact C. Palmer at 808-956-2324 for more information on ENSO-related climate data for the Pacific Islands.
Contact A. Wood at 405-447-8412 for more information about this issue of the Pacific ENSO Update


For further information, please contact:

Cynthia Palmer
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: cpalmer@soest.hawaii.edu

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


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