Pacific ENSO Update

1st Quarter 2001 - Vol. 7 No. 1


CURRENT CONDITIONS


In discussions below, we point out that most predictive models are suggesting the next El Niņo will occur in 2002. However, the background conditions resemble those of the similar period in 1997. In 1997, the triggers appeared in February and March. Thus, while most indicators suggest 2002 as the next El Niņo, we must closely monitor conditions over the next couple of months before eliminating 2001. Should conditions change, we shall issue special updates. Courtesy of Dr. Thomas Schroeder

During the last 3-4 months, the sea surface temperature (SST) distribution in the equatorial Pacific and the Southern Oscillation Index (SOI) indicated a resurgence of weak La Niņa conditions. Sub-surface sea temperatures in the eastern equatorial Pacific also became cooler. In the western equatorial Pacific, surface sea temperatures remained relatively constant over the past 6 months, slowly setting the stage for the next El Niņo event.

SST

After several months of "near normal" SSTs in the equatorial Central and extreme eastern part of the equatorial Western Pacific, SST anomalies fell to -0.6°C and -0.7°C respectively over the last few months. The La Niņa "cold tongue" that characteristically extends from the equatorial Eastern Pacific into the equatorial Western Pacific strengthened. This occurred right after the 2-year, 1998-2000 La Niņa had apparently come to an end. Despite this cooling, most Climate Models continue to indicate the rapid return to near zero SST anomalies by the boreal (northern hemisphere) spring of 2001. Most models also indicate a substantial warming with anomalies to near +1°C by the boreal summer of 2001. A few, however, suggest a slower change of the cooler than normal temperatures to warmer SSTs. At this time, it is too early to accurately predict when Central Pacific SST anomalies will become positive enough to declare the next El Niņo event. Thus, the current and predicted SSTs suggest that the next El Niņo will not occur until 2002 or later. The current weak La Niņa conditions are likely to persist into March.

Sub-surface sea temperatures in equatorial and near-equatorial parts of the Western North Pacific have stabilized to 2šC to 3°C above normal over the past 4 months. The depth of the warmer than normal sub-surface temperatures in some places is more than 400 feet, and warm anomalies up to 2°C extend down to 250 feet. Warm anomalies greater than 2°C also extend eastward to 170šW. In December, colder than normal sub-surface SSTs in the Central and Eastern Pacific were 5°C and 2°C, respectively, substantiating the recurrence of La Niņa conditions. Some warming of sub-surface temperatures in the Central Pacific appeared in January, suggesting some weakening of the cold event (La Niņa) intensity. Sub-surface SST profiles also suggest that another El N iņo is not likely until 2002 or later.

Sea level heights should be back to near normal values over the entire region. Local storm conditions, strong and persistent trade winds, nearby tropical cyclones, and favorable spring and fall astronomical conditions could all lead to short periods (lasting from days to weeks) of above normal sea levels and tides for all locations.

SOI

September to November 2000 SOI values hovered between +1.0 and +2.0, indicative of weak to moderate La Niņa conditions. The +2.0 value in November, however, was due to abnormally low pressures at Darwin resulting from a strong monsoon trough and tropical cyclone activity over northern Australia. While there were effects characteristic of weak La Niņa conditions, the large magnitude of the SOI was generally not reflected in the large-scale atmosphere across the Pacific. In December, Kapingamarangi had 23% above average rainfall, but in January, the island's rainfall total fell to nearly 50% (5.53") of normal values. Farther north in Kosrae, rainfall increased from 24% above normal in December to 115% above normal. In January, values were more characteristic of moderate La Niņa conditions. In addition, equatorial westerly winds failed to persist east of 140šE, and tropical cyclones developed farther west than normal, although farther to the east than in the previous two years. While monsoon and equatorial westerly winds occasionally extended east of 145šE, the duration of the events was short lived. Southern Hemisphere tropical cyclone activity has been below normal, with virtually all activity occurring in the Southwest Indian Ocean. Since January, the SOI has relaxed to around the +1 value, supporting a weak cold event.

We expect the SOI to move back toward normal values by summer, but La Niņa conditions will likely persist into March. With the SOI back to near neutral values, 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.

Figure 1 compares rainfall at selected Micronesian stations and at American Samoa for 1997 (strong El Niņo year), 1998 (El Niņo +1 (drought year)), 1999 (strong La Niņa year), and 2000 (moderate La Niņa year), and the long-term average. The figure illustrates that El Niņo years are generally average to wet for all locations, that El Niņo + 1 years are generally dry for all locations, and that La Niņa years are wetter than average at some locations, somewhat drier than average at other locations, and near average at still other locations. While this general pattern can be used as a first guess of the rainfall behavior that can be expected at the specific locations during the next ENSO cycle, the 1997-2000 rainfall behavior deviates from the long-term El Niņo-La Niņa rainfall behavior, which includes weak, moderate, and strong events. Also, the wet and dry periods are more exaggerated when -month periods instead of 12-month periods are considered. Users are referred to the NCEP/Climate Prediction Center Atlas No. 5 for these differences. Some aspects of the specific rainfall behavior will be further discussed in the individual Local Variability Summaries.

TROPICAL CYCLONE ACTIVITY

Tropical cyclone activity during 2000 in the Western North Pacific was below normal with 23 named tropical cyclones (named by the Japan Meteorological Agency (JMA)). The Joint Typhoon Warning Center (JTWC) identified 34 total tropical cyclones (named and unnamed) in 2000, less than the normal average of 40. Most of the Northern Hemisphere tropical cyclones developed in western longitudes or at high latitudes in response to La Niņa conditions early in the year and late in the year. To date, tropical cyclone activity in the Southern Hemisphere has been unusual, with little activity in the Southwest Pacific and the strongest activity in the Southwest Indian Ocean. Based on the expected resumption of near normal SST and SOI conditions by the boreal spring, normal tropical cyclone activity in the western North Pacific is anticipated for 2001. This means that Micronesia could see tropical cyclone activity from September until late-December. In eastern Micronesia, this activity should be limited to a few tropical storms and weak typhoons in the Marshall Islands and to the fringe effects of storms passing to the north of Pohnpei State and Kosrae State. In addition, Chuuk State, Yap State, Guam, and the CNMI could see additional activity from April to June. American Samoa is not expected to experience a significant tropical cyclone until the next El Niņo, although it could see a tropical depression or weak tropical storm in the January-April timeframe.

A new tropical cyclone name list was inaugurated for the Western North Pacific in 2000. A list of the names was given in Table 1 of our last (3rd Quarter) Pacific ENSO Update. A list of the storm names, their pronunciations, and their meanings is available at http://www.weather.gov.hk/informtc/sound/tcname2000e.htm.


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:While this report is called a "precipitation summary", there is little rainfall to talk about for the month of January. A weak cold front moved across Kaua'i and O'ahu on 1 January before stalling over Maui County on 2 January. Although weak, this system helped bring some rainfall to the very dry leeward areas of these islands. After the front dissipated, a ridge of high pressure entrenched itself over the island chain from 3 to 8 January. Moderate trades resumed on 9 January and persisted through the rest of the month. An upper level trough north of the islands on 14 January destabilized the airmass enough to enhance shower activity over the windward areas of Kaua'i. Rainfall was intense enough to prompt the issuance of an Urban and Small Stream Flood Advisory. No damages or injuries were reported.

The lack of December 2000 and January 2001 rainfall showed that Hawai'i was well on its way toward a fourth consecutive cool season with sub-par totals.

Kevin Kodama - Senior Service Hydrologist, NWSFO Honolulu, HI

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

American Samoa: Rainfall at Pago Pago Airport for the year 2000 was 117.24 inches or 96% of the long-term average. For October, November, and December, rainfall was 11.08 inches (103%), 9.04 inches (83%), and 10.41 inches (72%), respectively, amounting to 84% for the 3-month period. In January 2001, rainfall further decreased to 6.39 inches (51%). With fairly persistent southeast trade winds and weaker than normal SPCZ activity, east and southeast (windward) locations on Tuitilia likely received more rain.

The below normal rainfall experienced in the Samoa region for the November-December-January timeframe was due to a combination of stronger than normal subsidence and a westward shift of the SPCZ; both situations were likely associated with the recurrence of La Niņa. With equatorial SST anomalies and the SOI expected to return to near zero values by June, rainfall should also return to normal levels from June through the end of the forecast period. Figure 1 shows that for the strong El Niņo event of 1997, the wet El Niņo year (1997) and the dry El Niņo + 1 drought year (1998) both had less than the long-term average rainfall. It also shows that the La Niņa events of 1999 and 2000 both had near average rainfall. Based on this strong El Niņo case, "normal" rainfall should be above average to compensate for the below average El Niņo rainfall. However, for weak and moderate El Niņo events (which occur more often than strong events), the El Niņo year is very wet (similar to the pattern of Guam in Figure 1), and this excess rainfall more than compensates for the rainfall deficits observed in strong El Niņo years. Thus, "normal" rainfall for Pago Pago is actually slightly below (90-95%) the long-term average, as reflected in the new predictions. While it is too early to predict the next El Niņo, an event in 2002 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 east-west oriented portion of the SPCZ during the November-April timeframe, bringing heavy rains to the Samoan Islands as the cyclones move through the region.

Predicted rainfall for American Samoa from Feb 2001 through Mar 2002 is as follows:


Inclusive Period         % of long-term average
                              Samoa Region
Feb 2001 - May 2001                85%
Jun 2001 - Mar 2001                95%

- sources: UOG-WERI and PEAC

Guam/CNMI: Rainfall at Guam International Airport (GIA) during October, November, and December was 11.40 inches (95%), 5.16 inches (63%), and 8.90 inches (165%), respectively. This amounted to 108% of average values for the last quarter. For the year, GIA had 88.29 inches or 97% of the long-term mean. January measurements were only 2.90 inches (65%). Andersen Air Force Base (AAFB) measured 15.74 inches (122%), 6.31 inches (69%), and 9.99 inches (167%), or 119% of the average rainfall for the period. For all of 2000, AAFB had 101.30 inches or 103% of its long-term mean. January rainfall was 3.27 inches or only 57% of the average.

October, November, and December rainfall at Saipan International Airport (SIA) was 10.96 inches (101%), 5.39 inches (93%), and 5.84 inches (152%), or 115% of the average for the period. For the year 2000, SIA experienced 70.29 inches of rain or 95% of the long-term average. Precipitation in January was a dry 1.39 inches (43%). As is the usual case, Capitol Hill was somewhat wetter with 86.51 inches average. For October, November, and December, measured rainfall at Capitol Hill was 9.92 inches (83%), 6.40 inches (88%), and 8.54 inches (178%). January rainfall there was 4.56 inches (114%). Rainfall amounts for October, November, and December at the Tinian Airport were 16.76 inches (140%), 7.16 inches (98%), and 6.92 inches (144%), respectively. The 3-month rainfall for Tinian Airport was a wet 127%, while the annual rainfall was 91.03 inches (109%). January rainfall there was a meager 2.62 inches (66%). At Rota Airport, October, November, and December rain amounts were 16.18 inches (128%), 4.91 inches (57%), and 8.98 inches (176%). This gave a 3-month average of 120%. For the 2000 year, Rota had 98.31 inches (104%). In January, the amount was a wetter than normal 6.01 inches (114%). On the northern part of Rota, at the beautiful Rota Resort and Country Club, the NASA TRMM network there recorded 107% of that at the Airport in the period October-December, but only 92% of that at the Airport for the entire year.

Rainfall for Guam and the CNMI is expected to return to normal by June. Figure 1 illustrates that during the last ENSO cycle, Guam and the CNMI were wet during the El Niņo year and dry during the El Niņo + 1 year. However, 1997 was the second wettest year recorded on Guam, and not characteristic of El Niņo years, which for the Mariana Islands, can be wetter than, drier than, or similar to the average. Unlike much of Micronesia, La Niņa-induced dry season rains at these locations can be wet, dry, or near average as in 1999 and 2000. While El Niņo and La Niņa years, over the long run, tend to be average to slightly above average, the El Niņo + 1 year is usually very dry. To compensate for this, the non-ENSO years should be slightly wetter than the average. This should be expected since monsoon and tropical cyclone activity are normally greater during these years. Thus "normal" rainfall for the Mariana Islands is somewhat greater than the long-term average or about 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 affect Guam and the CNMI during this forecast period. Tropical cyclone activity should also return to normal. Thus, the Mariana Islands can expect typhoon threats primarily from September through December. Most will approach from the east-southeast. A secondary period of occurrence is in April and May. While typhoons in these months are more rare, they can be very intense, as were the cases with Pamela in May1976 and Andy in April 1989.

Predicted rainfall for the Mariana Islands from Feb 2001 through Mar 2002 is as follows:


Inclusive Period         % of long-term average
                      Guam/Rota       Saipan/Tinian
Feb 2001 - May 2001      80%               90%
Jun 2001 - Mar 2002     110%              110%

- sources: UOG-WERI

Yap State: Northern Yap State was quite wet for the three months, October through December. The weather station at the Yap Airport recorded 18.01 inches (150%) in October, 9.99 inches (110%) in November, and 12.29 inches (137%), or 132% of normal rainfall for the three months. For the entire year, Yap had 143.66 inches of rain or 120% of the long-term average. In January, only 5.02 inches of rain (68%) fell there. Ulithi Atoll had 115.21 inches or 113% for 2000. October, November, and December rainfall amounts on Ulithi were 11.02 inches (108%), 10.91 inches (142%), and 16.49 inches (216%) or 155% for the 3-month period. January was drier with a mere 1.98 inches (32%). Farther south at Woleai Atoll, rainfall totaled 141.72 inches (102%) for the year. In October, rainfall was 11.86 inches (87%). In November, it was 11.57 inches (107%), and in December, it was 12.48 inches (109%), for a near normal 3-month average of 101%. Rain on the atoll in January was measured at 10.98 inches (103%).

Rainfall for Yap State is expected to be about 100%-110% of the long-term average, depending on location. Figure 1 indicates that the La Niņa-associated rainfall excess more than compensates for the El Niņo-induced rainfall deficit. However, in general, this is not the case when all events in the last 30 years are considered. Thus, normal rainfall for Yap State must make up this deficit, and should therefore be greater than 100% of the long-term average. This additional rain is due to the active monsoon and the 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 late September through mid-December, while southern islands can be affected from mid-October until late-December. There could also be a threat of storms in May and June.

Predicted rainfall for Yap State from Feb 2001 through Mar 2002 is as follows:


Inclusive Period                % of long-term average
                             Yap               Outer Atolls:
                            Island       S.of 8·N     N. of 8·N
Feb 2001 - Sep 2001           95%          100%          90%
Oct 2001 - Mar 2002          110%          115%         110%

- sources: UOG-WERI

Chuuk State: During 2000, Chuuk lagoon islands were wetter than normal with about 119% of normal rainfall. Weno Island had 160.07 inches for the year. During October, November, and December, the weather station at Weno Island measured 15.89 inches (118%), 11.02 inches (107%), and 17.64 inches (162%). This amounted to129% of the norm for the 3-month period. In January, 12.61 inches (118%) were recorded. The outer islands to the south and west were slightly drier than normal for the year and considerably drier for the last quarter of the year. In the Mortlocks at Lukunoch, rainfall for the year was 129.79 inches or 97% of normal. October, November, and December rainfall there was 11.42 inches (85%), 4.64 inches (45%), and 7.73 inches (71%) for the respective months. The 3-month average was only 67%. January rain was 14.64 inches (137%). Year 2000 rain in Polowat was considerably less than in other parts of the State with 104.53 inches (87%). Rain in October, November, and December was 7.04 inches (59%), 5.39 inches (58%), and a wetter 10.69 inches (116%) in the respective months, giving a 3-month average of only 78%. January saw increased, but continued below normal, rainfall return to Polowat with 7.58 inches (95%).

Rainfall for all of Chuuk State is expected to be slightly wetter than normal, but with high month-to-month variability. Figure 1 shows that the heavy La Niņa rainfall (1999-2000) did not quite make up for the below normal El Niņo-induced rainfall (1997-1998). 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. This is due to increased monsoon activity and to some increased tropical cyclone activity. Tropical cyclone activity should also return to normal. This means that Chuuk will have a higher risk of getting a tropical storm or typhoon, primarily during the months of October, November, and December. Some risk will also occur in April and May as well.

Predictions for Chuuk State from Feb 2001 through Mar 2002 are as follows:


Inclusive Period               % of long-term average
                        Chuuk         Outer Atolls
                        Lagoon    Southern    Western
Feb 2001 - Sep 2001     100%       100%         90%
Oct 2001 - Mar 2002     110%       115%        110%

- sources: UOG-WERI

Pohnpei State: The year 2000 for all of Pohnpei State was slightly wetter than normal to near normal. Observations from Pohnpei Island suggest that coastal areas of the island were wetter than the interior locations, but this is not normally the case. Thus, for whatever reason, some of the interior observations may reflect lower values of rainfall than actually occurred. October, November, and December rainfall measured at the weather station at Kolonia was 15.14 inches (91%), 10.35 inches (66%), and 21.95 inches (144%). This amounted to 100% of average precipitation. For the year, the Weather Station had 205.43 inches or 109% of the long-term average. The weather station also measured 21.71 inches (166%) in January 2001. At Pingalap, observed rainfall in October, November, and December was 14.74 inches (100%), 12.31 inches (86%), and 15.52 inches (116%) respectively, for a 3-month amount of 101%. For the entire year, Pingalap experienced 183.55 inches or 103% of the long-term average. January kicked off the new year with 26.69 inches (215%). At Nukuoro, October-December precipitation amounts were 13.83 inches (129%), 17.01 inches (142%), and 7.58 inches (63%), respectively. The 3-month period was 111% of the normal value. For the year, Nukuoro had 186.47 inches, which is 25% above the long-term average. Rainfall in January 2001 was 17.71 inches (150%) for the island. With the disappearance of weak to occasional moderate La Niņa influences, rainfall increases that began in May continued through the end of the year at Kapingamarangi. October, November, and December measurements there were 4.82 inches (100%), 8.27 inches (101%), and 10.88 inches (124%), respectively, giving a 3-month average of 108%. For the year, Kapingamarangi measured only 77.28 inches or 70%, a result of La Niņa-induced subsidence early in the year along the Equator. January rainfall for Kapingamarangi fell to 5.53 inches (53%) as the newly developed La Niņa reached more western longitudes.

Figure 1 shows that the heavy La Niņa rainfall (1999-2000) does not make up for the below normal El Niņo-associated rainfall (1997-1998). 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 except Kapingamarangi is expected to be above normal through March, near normal through September, and then somewhat above normal for the remainder of the forecast period. Kapingamarangi will be drier than normal through March or April due to lingering La Niņa effects, and then will become wetter. 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 and periods of strong westerly winds for Pohnpei State during the winter of 2001-2002 and the spring of 2002. Oct 2001-Mar 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 from typhoons passing to the north.

Predicted rainfall for Pohnpei State from Feb 2001 through Mar 2002 is as follows:


Inclusive Period          % of long-term average
                     Pohnpei           Outer Atolls:
                     Island    Eastern    Southern    Equatorial
Feb 2001 - Mar 2001   150%      175%        150%         70%
Apr 2001 - Sep 2001   100%      100%        100%        100%
Oct 2001 - Mar 2002   110%      115%        120%        125%

- sources: UOG-WERI

Kosrae: During the last quarter of 2000, wet weather returned to Kosrae. Observers at Kosrae Airport recorded 19.92 inches (123%), 116.65 inches (105%), and 18.39 inches (127%) for October, November, and December, which amounted to 118% of the long-term average rainfall for the period. This resulted from a very persistent tradewind trough anchored between 4šN and 5šN across the western North Pacific. For the year 2000, the Kosrae Airport had 208.01 inches or 101% of the long-term average. In January, the Airport experienced a considerable increase with 31.01 inches (215%). For all of 2000, Tofol was the wettest Kosrae State location that measures rain with 235.61 inches (13% wetter than the Airport), while Tafunsak was the driest with 194.19 inches (7% drier than the Airport). Utwa fell between the other stations with 214.46 inches (3% wetter than the Airport). During January 2001, Tofol measured 35.65 inches of rain.

Figure 1 shows that the heavy La Niņa rainfall (1999-2000) does not make up for the below normal El Niņo-associated rainfall (1997-1998). 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. Rainfall for Kosrae is expected to be above normal through March, near normal from April through September, 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 and periods of strong westerly winds for Kosrae State during the winter of 2001-2002 and the spring of 2002. Oct 2001-Mar 2002 rainfall predictions reflect this possibility. Kosrae should not experience any tropical cyclones until the next El Niņo event begins.

Predicted rainfall for Kosrae State from Feb 2001 through Mar 2002 is as follows:


Inclusive Period     % of long-term average
Feb 2001 - Mar 2001            175%
Apr 2001 - Sep 2001            100%
Oct 2001 - Mar 2002            115%

- sources: UOG-WERI

Republic of Palau: After an extremely dry September (only 3.10 inches (26%) at Koror), the rains returned to Palau. Rainfall at Koror during October, November, and December was 13.49 inches (97%), 14.27 inches (126%), and 18.87 inches (158%), respectively. The 3-month average was 127% of normal. For the entire 2000 year, the Weather Station at Koror measured 161.21 inches or 109% of the long-term average. In January, rainfall decreased to only 6.21 inches (58%). For the 3-months of October, November, and December, rainfall at the Mariculture Center was 3% less than that at the Weather Station and at Nekken Forestry was 2% more than that at the Weather Station. January rainfall at Mariculture and Nekken Forestry was wetter with 8.65 and 9.72 inches respectively. Farther south at Peleliu, conditions were slightly wetter with 15.38 inches (111%) in October, 16.46 inches (146%) in November, and 18.02 inches (151%) in December. This produced a 3-month average of 136%. For the year, Peleliu had 153.74 inches of rain, which is 104% of the long-term average. In January, the island had 12.38 inches or 116% of that expected.

Figure 1 shows that the heavy La Niņa rainfall (1999-2000) did not make up for the below normal El Niņo-associated rainfall (1997-1998). 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 return to near normal. 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 swells from typhoons passing to the north could cause dangerous surf.

Predicted rainfall for Palau from Feb 2001 through Mar 2002 is as follows:


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

- sources: UOG-WERI

Republic of the Marshall Islands (RMI): After a drier than normal spring and summer, near normal rainfall returned to the Republic of the Marshall Islands (RMI). Most of the increased rainfall was the result of the reformation of a well-developed tradewind trough. During October, November, and December, the Majuro weather station (representative of the southern islands) measured 12.27 inches (89%), 15.03 inches (117%), and 9.20 inches (78%). For the period, the average was 95%. For the year 2000, the total rainfall for Majuro was 135.33 inches or 103% of the long-term average. In January 2001, rainfall was 5.73 inches, or 68% of normal. Kwajalein rainfall (representative of the central islands) during the fourth quarter increased to near normal values, after a dry spring and summer. Rainfall at Kwajalein (and nearby Ebeye) was 13.85 inches (116%) in October, 6.75 inches (63%) in November, and 11.05 inches (136%) in December. This was an average of 105% for the period. For the entire year of 2000, Kwajalein had 98.02 inches or 96% of the long-term average. In January, amounts rose to 3.53 inches or 77% of that normally expected. Rainfall amounts at Laura were slightly less than at Majuro. Ailingalaplap had considerably less rainfall than Majuro, Kwajalein, and Jaluit during the last quarter of 2000 and also for the entire 2000 year. In October, November, and December, Ailingalaplap experienced 9.46 inches (73%), 7.30 inches (62%), and 11.46 inches (115%), respectively, and for the year, experienced 86.93 inches (74%). Jaluit's rainfall was greater than that in the rest of the Marshalls. For the last three months of the year, Jaluit had 9.29 inches (67%), 15.46 inches (121%), and 7.82 inches (66%) respectively, for a 3-month value of 85%. For the year, 147.74 inches (112%) fell on the atoll. Wotje was the driest of the locations that measured rainfall during the year. In the October-December timeframe, rainfall amounted to a 3-month average of only 66%. For 2000, Wotje had 63.32 inches or 65% of the long-term average. In January, rainfall ranged from 122% of normal at Ailingalaplap to 54% at Wotje. Observations were not available from Utirik; however, satellite imagery indicated that it was likely the driest part of the Marshall Islands.

Figure 1 shows that the above average La Niņa rainfall (1999-2000) did not make up for the below average El Niņo-associated rainfall (1997-1998) at Majuro, and even less so at Kwajalein. This is consistent with observations over the last 30 years, which also show the same pattern for weak, moderate, and strong ENSO events. Thus, normal years and years leading into another El Niņo should be wetter than the long term average to make up for the El Niņo-related rainfall deficit. As a result, 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 and periods of strong westerly winds for the south and central Marshall Islands during the winter of 2001-2002 and the spring of 2002. Nov 2001-Mar 2002 rainfall predictions reflect this possibility. Tropical cyclone activity for the Marshalls should return to normal, meaning that Wake and Enewetok could see typhoons 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 next El Niņo event.

Predicted rainfall for the RMI from Feb 2001 through Mar 2002 is as follows:


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

- sources: UOG-WERI


APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 15 February 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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