Pacific ENSO Update

2nd Quarter 2000 - Vol. 6 No. 2


CURRENT CONDITIONS


SST

Average March equatorial sea surface temperature (SST) anomalies in the Central Pacific [Niño 3.4 region (170W-120W)] were -1.0ºC (-1.8ºF), corresponding to a weak La Niña event. However, the event was moderate from November through February. This is the second year of La Niña conditions, and this current event has been very similar to the La Niña of 1998-1999 in terms of SST distribution and patterns. Despite the weakening of the event, near-equatorial areas east of 160ºE and Southwest Pacific areas north of 8ºS and east of 170ºE should see a continuation of significantly drier than normal conditions until the July-August timeframe. Much of Micronesia between 3ºN and 10ºN will be somewhat wetter than normal through the same time period. We expect co nditions to return to normal by August or September.

SST anomalies in the Central equatorial Pacific [Niño 3.4 region (170W-120W)] appeared to reach a peak in January, where they were -1.8ºC (-3.2ºF). By February they had fallen to -1.5ºC (-2.7ºF), and by March, they had fallen to -1.0ºC (-1.8ºF). The are a of lower than normal equatorial SST has continued to shrink over the last 3 months. March TOGA buoy data indicate that Central Pacific equatorial sub-surface ocean temperature anomalies warmed considerably over the last 3 months, receded to the east, and became shallower, with maximum anomalies of -4ºC (-7.2°F) at a depth of 25 m near 90ºW. This provides support for phasing out the La Niña by the boreal fall. The buoy data also indicate that Western Pacific equatorial sub-surface ocean temperature anomaly has stabilized at about +4ºC (+7.2ºF) and have become deeper, with maximum values at 150-200 m deep. These temperatures have not spread eastward over the last 2 months, but have spread westward beyond 140ºE. Conditions are setting up for another El Niño event, but it is too early to tell whether this will occur in 2001 or later. Will we see a third year of La Niña conditions as we saw from 1908-1910 and from 1954-1956? At this point we do not have the ability to tell. In March, climate model guidance was unclear, with a few models predicting warmer than normal equatorial SSTs by early 2001, a few predicting near normal conditions by the boreal fall, and yet another, the Hybrid Coupled Modeled (HCM), predicting a continuation of La Niña conditions into to early 2001. Given the model guidance and the latest trends/changes in SST behavior, we expect neutral conditions by fall.

Our predictions during this quarter are built on the premise that conditions will become normal by the boreal fall and will remain so into mid 2001. There is some chance of an El Niño developing in 2001 and some chance of a recurrence of La Niña conditions in 2001. However, we do not yet have the skill or knowledge to quantify these possibilities.

SOI

The Southern Oscillation Index (SOI) continued to hover between +0.7 and +1.6 during the past 5 months, suggesting a weak to moderate La Niña event. In March, the SOI fell to about +1.0 from a high of +1.6 in February, but the rose again in April to +1. 4. This positive SOI has been consistent with observed rainfall patterns in the equatorial Central and Western Pacific. Low-level equatorial easterly winds have been stronger than normal, a condition consistent with reduced rainfall east of 160ºE. Subsidence is generally greater than normal over the equatorial Pacific region, as reflected by strong downward vertical motion fields and much lower than normal low-level relative humidity values. With cooler SSTs remaining along the equator, reduced evaporation coupled with strong subsidence will make conditions drier than normal in the equatorial regions. Weakening trade winds over the past 2 months should weaken the trade wind trough near the Date Line. As a result, rainfall has diminished in the southern Marshall Islands and in northern Kiribati from the well-above normal amounts experienced in January and February.

The March 2000 SOI value of +1.0 standard deviation was well below the February peak value of +1.6. The positive SOI is in phase with the negative SSTs, and is consistent with observed rainfall patterns. The equatorial SOI between the Eastern Pacific and Indonesia is even more indicative of La Niña conditions. Upper level circulation patterns from 15°N to15°S over the Central and Western Pacific tropics have been more convergent than normal, which has also been conducive to below normal rainfall in equatorial areas.

Shear lines (washed out cold fronts) in the western North Pacific have been weaker and much less frequent than expected. This kept most of the rainfall south of 10ºN, making conditions in the Mariana Islands, at northern Yap State Islands, and in the northern Marshall Islands (north of Kwajalein) drier than expected. Most Micronesian Islands between 4ºN and 9ºN-10ºN will likely continue to have above normal rainfall into June or July. Near equatorial islands south of 4ºN and east of 160ºE will be considerably drier than normal, although conditions should improve by May or June. The Mariana Islands are now expected to have slightly below normal rainfall through June, although upper level cyclonic cells in the Tropical Upper Tropospheric Trough (TUTT) should bring periods of heavy rain and thunderstorms through the islands. Month-to-month rainfall will, however, be highly variable.

In the Southern Hemisphere, the east-west oriented portion of the South Pacific Convergence Zone (SPCZ) hovered across 10ºS-12ºS in an off and on manner from January-March. Lately, the SPCZ has shown some movement north of 10ºS. Monsoon activity across Australia and into the Southwest Pacific during 1999-2000 has been relatively weak and will likely remain so until October 2000. Tropical cyclone activity in the region has been below normal (but above normal in the South Indian Ocean), typical of La Niña conditions. The north-south oriented portion of the SPCZ has been anchored near 160ºW, but has continued to be highly variable in its organization. The position and intensity of the SPCZ will likely keep rainfall in the Samoa region near normal to slightly below normal. Month-to-month rainfall there will be variable, fluctuating with the position of the SPCZ.

TROPICAL CYCLONE ACTIVITY

Western North Pacific tropical cyclone (TC) activity in 1999 was 89% of normal (34 versus 38), with most of these being weaker and smaller than normal. Most of the 1999 TCs there formed west of 135ºE, characteristic of La Niña periods. Stronger than normal trade winds, subdued monsoon activity, and a poorly developed near-equatorial trough all contribute to the low output of strong TCs and to the far-western average longitude of development. With the resurgence of La Niña conditions in 2000, TC development could again be delayed and pushed farther to the west. TC activity for Micronesia could affect islands west of 150ºE in May, but most areas will probably not be affected until September 2000. Significant Southern Hemisphere TC activity will likely remain west of the International Date Line. Thus, American Samoa and islands east of the Date Line should not experience damaging TC activity until the next El Niño event.

OTHER COMMENTS

Despite the similarities of the 1998-1999 La Niña event and the 1999-2000 La Niña event, there were many differences between the observed rainfall in the first 3 months of 1999 and in the first 3 months of 2000. These differences were especially large in certain areas such as American Samoa, the Marshall Islands, Nukuoro (Pohnpei State, FSM), and Palau. The differences in January-March 1999 rainfall and January-March 2000 rainfall are shown in Table 1 and in Figure 3. Note that small zonal and small meridional shifts in the position of the trade wind trough can cause large differences in the rainfall. This highlights the high variability that can occur during two very similar La Niña events, and underscores the difficulty of producing accurate rainfall predictions during La Niña.

As oceanic and atmospheric conditions return to normal, our skill at predicting variations in rainfall for specific locations will decrease. Rainfall will return to near "normal" values, likely with high month-to-month variability. We will vigilantly monitor conditions as they set up for the next El Niño event or for a possible follow-on La Niña event. While an El Niño event could occur as early as April 2001, at this time, April 2002 or later seems more likely.


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:The weather pattern for the beginning of April reminded the residents of Hawai'i that they are still in the cool season with two shear lines impacting the islands on 1 and 3 April. Both shear lines were accompanied by very strong trade winds from 1 through 5 April. The 3 April shear line also brought enough rainfall to produce minor flooding over portions of north Kaua'i. These weather systems were followed by a weak cold front that moved over the island chain on 8 April. A period of wet trades in the fresh to strong range followed the cold front from 9 to 11 April. Trade winds, mainly in the moderate to fresh range, persisted for the rest of the month. A weak shear line embedded within the trades arrived over the islands on 17 April with only limited amounts of associated rainfall. An impressive looking (in the satellite images) upper level low passed south of the island chain from 20 to 23 April with no significant effect on the rainfall.

Kevin Kodama - Senior Service Hydrologist, NWSFO Honolulu, HI

For a more complete summary, and the county by county wrap-ups, please see the April 2000 Precipication Summary from the National Weather Service Honolulu Weather Forecast Office.

American Samoa: Rainfall for the next year for the Samoa region is expected to be near normal until September, then slightly below normal well into 2001. The area can expect high month-to-month variability in rainfall. Strong tropical cyclone activity in the region is not expected to recur until the next El Niño event, although some weak tropical cyclones could develop in the monsoon trough to the north of the islands.

Rainfall in the Samoa region was slightly above normal from January-March 2000. At Pago Pago International Airport, January rainfall was 13.43 inches (107%), February rainfall was 13.54 inches (106%), and that in March, jumped up to 18.24 inches (162%). For the quarter, rainfall averaged 125% of normal. The north-south oriented portion of the South Pacific Convergence Zone (SPCZ) remained anchored near 160°W, but intensified during the period. This brought longer periods of heavy rainfall to the Samoa region, especially in March. This occurred despite some intensification of the current La Niña, which weakened the east-west oriented portion of the SPCZ, keeping conditions drier than normal in the northern Cook Islands, Tokelau, and Tuvalu. The east-west portion of the SPCZ has already shown some signs of moving north of 10ºS, and this should bring some relief of drought conditions in these locations. While some computer models indicate the continuation of La Niña conditions into late 2000, e expect atmospheric conditions to moderate with a return to near normal by September. At this time, we expect rainfall to be about 90% of the long-term average.

While a few developing TCs could affect the Samoas, strong tropical storm-force winds or hurricane-force winds are not likely until the next El Niño.

Predicted rainfall for American Samoa from Apr 2000 through Jun 2001 is as follows:


Inclusive Period         % of long-term average
                              Samoa Region
Apr - Sep 2000                    105%
Oct 2000 - Jun 2001                90%

- sources: UOG-WERI and PEAC

Guam/CNMI: After a dry January, rainfall for Guam and the CNMI moved closer to normal in February and March. However, with continued La Niña conditions into summer, we expect rainfall to be slightly below normal into summer. By August, rain amounts should then return to normal. Tropical cyclone and monsoon activity may be delayed by 1-2 months due to La Niña, but they are also expected to return to normal by August.

As anticipated in our last Newsletter, Jan-Mar 2000 rainfall at Guam International Airport (Tiyan) was near normal to slightly wetter than normal. In January, the Airport received 2.79 inches (63%), in February 4.92 inches (132%), and in March 4.05 inches (136%). For the 3-month period, rainfall averaged 110%. At Andersen Air Force Base (AAFB), January rainfall was 3.40 inches (60%), February rainfall was 5.90 inches (113%), and March rainfall was 5.06 inches (124%). For the three months, rainfall averaged only 99%.

Saipan was drier than Guam during the first quarter of the year. At Saipan International Airport (SIA), January rainfall was 1.07 inches (33%), February rainfall was 3.02 inches (126%), and March rainfall was 2.50 inches (68%). This gave a 3-month average of 76%. As is normal, Capitol Hill was wetter. There, January rain amounted to 2.60 inches (65%), February rain measured 6.08inches (203%), and March rain totaled 3.71 inches (148%). This created a 3-month average of 139%.

As expected, rainfall at Rota International Airport was similar to that at Guam, while that at Tinian International Airport was similar to Saipan. At Rota, January rainfall was 2.01 inches (38%), February rainfall was 8.38 inches (179%), and that for March was 4.07 inches (110%). For the three months, the average was 109%. The NASA rain gauges at the Rota Resort and Country Club indicated that northern Rota was drier with 1.05, 6.68, and 2.86 inches for the respective months-about 70% of that at the Airport. At Tinian, rainfall was 1.27 inches (32%), 6.17 inches (206%), and 2.23 inches (89%) for the respective months, giving a 3-month average of about 109%.

We expect the Mariana Island to have slightly below normal rainfall from April-July as a result of the current La Niña, which is expected to delay persistent monsoon and tropical cyclone activity. To date, shear lines affecting the Mariana Islands have been less frequent than expected. This kept disturbances moving south of the island, making the area somewhat drier than anticipated for the first 4 months of 2000.

At this point, we expect western North Pacific tropical cyclone activity to return to normal by August, and to threaten the Mariana Islands by September. If the monsoon surges eastward to Chuuk, a tropical cyclone could develop there and affect the Mariana Islands in May.

Predicted rainfall for the Mariana Islands from Apr 2000 through Jun 2001 is as follows:


Inclusive Period         % of long-term average
                      Guam/Rota       Saipan/Tinian
Apr - Jul 2000           90%               90%
Aug 2000 - Jun 2001     100%              100%

- sources: UOG-WERI

Yap State: After a wetter than normal January-March 2000, Yap State is expected to have rainfall slightly drier than normal until July. Tropical cyclone activity is expected to be back to normal by August, but some tropical cyclone activity could also occur in May.

Rainfall at Yap Airport during January, February, and March was 4.49 inches (61%), 4.64 inches (78%) and 9.77 inches (164%), respectively. This made the first quarter of the year 101% of normal. Gilman and Rumung were considerably wetter than the Airport, Tamil and North Fanif were about the same, and Luweech was drier than the Airport. At Ulithi, January had 4.37 inches (70%), February had 6.86 inches (135%), and March had 6.36 inches (125%)-110% of normal. Farther south at Woleai Atoll, rainfall was 10.08 inches (94%), 5.97 inches (80%), and 8.32 inches (100%) for the first three months of the year respectively-91% of normal. Table 1 and Figure 3 show that the region had similar rainfall during the first 3 months of the 1999 La Niña and the 2000 La Niña.

Shear lines (washed out cold fronts) did not move through Yap State as expected. This eliminated normal shear line rainfall, and more critically, it prevented most disturbances that developed southeast of the main island from taking a more northward track over the island. This kept the area drier than anticipated for the first 4 months of 2000. We expect conditions to be somewhat drier than normal for all of Yap State, but especially for southern portions as the eastward surge of the monsoon is delayed by La Niña. Cyclonic cells in the Tropical Upper Tropospheric Trough (TUTT) will bring intermittent disturbances and thunderstorms to the more northern islands. The monsoon, once established, could be active into November, bringing several episodes of heavy late-season rainfall.

Tropical cyclone activity should return to normal in the western North Pacific by August. The greatest tropical cyclone threats for Yap State will be from mid-September-December. The monsoon could surge into the area in May and June, creating the potential for a tropical cyclone in May.

Predicted rainfall for Yap State from Apr 2000 through Jun 2001 is as follows:


Inclusive Period                % of long-term average
                             Yap               Outer Atolls:
                            Island       S.of 8·N     N. of 8·N
Apr - Jun 2000                95%           90%          95%
Jul 2000 - Jun 2001          100%          100%         100%

- sources: UOG-WERI

Chuuk State: Chuuk State was considerably wetter than normal during the first three month of 2000. Conditions for the southeastern islands should continue to be slightly wetter than normal until July. Northwestward islands should be slightly drier. Afterward, we expect rainfall to return to normal. Tropical cyclone activity should return to normal by August, and could affect Chuuk State from October-December. There is some chance for a tropical cyclone to develop near Chuuk in May if the monsoon temporarily surges in to the region.

Chuuk State was wetter than normal during the first three months of 2000, primarily as a result of the La Niña-induced wet February and March (see Table 1 and Figure 3). The continuation of La Niña is also expected to keep conditions at the southeastern islands wetter than normal into early summer. From January through March, Chuuk Airport had 7.71 inches (72%) of rain, 12.54 inches (203%), and 14.73 inches (177%), respectively. This is a 3-month average of 151%. At Lukunoch, January had 11.39 inches (107%) of normal rainfall, February had a very wet 22.72 inches (368%), and March saw 10.82 inches (130%)-a 3-month average of 202%. Polowat was somewhat drier than the rest of Chuuk State, with 7.79 inches in January (97%), 4.49 inches in February (72%), and 10.39 inches in March (166%).

The current La Niña is expected to keep the region between 3ºN and 10ºN and east of 150ºE wetter than normal through spring due to disturbances that develop in the trade wind trough. Rainfall should return to normal by July. The monsoon could surge into the region in May and June, and could be active into late October or early November, bringing additional episodes of heavy rainfall. Tropical cyclone activity should be back to normal by August, and could affect Chuuk State in the October-December timeframe. A tropical cyclone could also develop in May if the monsoon surges into the region.

Predicted rainfall for Chuuk State from Apr 2000 through Jun 2001 is as follows:


Inclusive Period               % of long-term average
                        Chuuk         Outer Atolls
                        Lagoon    Southern    Western
Apr - Jun 2000          110%       115%         90%
Jul 2000 - Mar 2001     100%       100%        100%

- sources: UOG-WERI

Pohnpei State: Rainfall at Pohnpei and Pingalap was much wetter during the first quarter of 2000. Farther south, Nukuoro was slightly wetter than normal, while Kapingamarangi was much drier than normal. Except for near equatorial areas, Pohnpei State is expected to be wetter than normal into July due to the ongoing La Niña, then will have rainfall amounts closer to normal for the remainder of the period. Tropical cyclone activity in Micronesia is expected to be back to normal by August, but significant tropical cyclones will not likely threaten Pohnpei State until the next El Niño begins to develop.

La Niña-associated rainfall at Pohnpei Island was considerably heavier from Jan-Mar 2000 than from Jan-Mar 1999. Table 1 and Figure 3 show the differences in rainfall distribution for the 3-month periods in 1999 and 2000. During the first three months of 2000 at the Pohnpei Weather Station, January rainfall was 19.50 inches (149%), February rainfall was 18.63 inches (173%), and March rainfall was 21.68 inches (160%). This amounted to 160% for the period. Other parts of the island were drier, with most other locations on the island experiencing about 95% of that measured at the weather station. This is probably the result of some missing measurements.

As in the first three months of 1999, Pingalap was considerably wetter than normal for the same period of 2000. In January, Pingalap had 19.27 inches (156%), in February it had 20.55 inches (168%), and in March the island experienced 25.84 inches (178%). This produced an average of 167% for the quarter. Nukuoro was not nearly as wet for the period as in the same quarter of 1999. During January-March, the atoll had 12.60 inches (107%), 19.18 inches (188%), and 12.66 inches (93%), a 3-month average of 129%. This was considerably below the amounts experienced in the same period of 1999 (see Table 1 and Figure 3).

The resurgence of La Niña brought very dry conditions back to near equatorial areas of the western Pacific. Rainfall measurements on Kapingamarangi were 3.59 inches (34%) in January, 2.51 inches (24%) in February, and 3.73 inches (27%) in March. This was a 3-month average of only 3.28 inches (28%).

The current La Niña is expected to keep the region between 3ºN and 10ºN wetter than normal into the summer due to disturbances that develop in the trade wind trough. Upper level winds associated with the Tropical Upper Tropospheric Trough will enhance these disturbances. Equatorial areas east of 160ºE will be considerably drier than normal. By July, rainfall there should be moving back to more normal values. Tropical cyclones could affect northern parts of Pohnpei State in November or December, but the greatest threat will occur with the development of the next El Niño event. There is a chance that Pohnpei State could see some strong westerly winds by late fall, producing heavier than predicted rains and strong westerly winds. However, it is too early to tell if this scenario will develop.

Predicted rainfall for Pohnpei State from Apr 2000 through Jun 2001 is as follows:


Inclusive Period          % of long-term average
                     Pohnpei           Outer Atolls:
                     Island    Eastern    Southern    Equatorial
Apr - Jun 2000        120%      125%        110%         40%
Jul - Sep 2001        105%      105%        105%         80%
Oct 2000 - Jun 2001   100%      100%        100%        100%

- sources: UOG-WERI

Kosrae: Rainfall on Kosrae was significantly wetter than normal during the first 3 months of 2000. Because of the continuing La Niña, Kosrae State is expected to be wetter than normal into July, then will have rainfall amounts closer to normal for the remainder of the period. Tropical cyclone activity is expected to be back to normal in the western North Pacific by August, but significant tropical cyclones will not likely threaten Kosrae State until the next El Niño begins to develop.

La Niña conditions gave Kosrae another extremely wet January-March. Kosrae Airport had 19.49 inches (135%) in January, 18.40 inches (113%) in February, and 23.96 inches (176%) in March. This was a 3-month average of 20.5 inches (141%) compared with an average of 19.60 (123%) for the same three months of 1999. For the January-March 2000 period, Utwa, Tofol, and Tafunsak were 10-15% wetter than the Airport. In fact, Tofol was the wettest area with 25.88 inches in February and 28.72 inches in March. Kosrae's heavy rainfall was primarily due to disturbances that developed in the trade wind trough to the east and tracked primarily over Kosrae.

We expect Kosrae to have wetter than normal rainfall until July in response to the current La Niña, which is expected to keep the region between 3ºN and 10ºN wetter than normal due to disturbances that develop in the trade wind trough. This convection could be enhanced by the upper level effects of the Tropical Upper Tropospheric Trough (TUTT). Afterwards, rainfall should return to near normal values from July 2000 through June 2001. Tropical cyclone activity should not pose a direct threat to Kosrae until the next El Niño begins to set up. Since current western Pacific sub-surface ocean temperatures have warmed considerably, there is a chance that Kosrae could see some strong westerly winds by late fall, producing heavier than predicted rains and strong westerly winds. However, it is too early to predict such activity at this point.

Predicted rainfall for Kosrae State from Apr 2000 through Jun 2001 is as follows:


Inclusive Period     % of long-term average
Apr - Jun 2000                 130%
Jul - Sep 2000                 105%
Oct 2000 - Jun 2001            100%

- sources: UOG-WERI

Republic of Palau: The Republic of Palau had above normal rainfall during the first quarter of 2000. We expect conditions to be wetter than normal for the Island Nation through July. By August, rainfall amounts should return to near normal. Tropical cyclone activity could threaten islands north of Angaur in May and from October through December.

Palau was much wetter than normal during the first three months of 2000. The Koror Weather Station had January rainfall of 13.16 inches (123%), February rainfall of 20.17 (221%), and March rainfall of 6.63 inches (81%)-an average of 142% of normal for the 3-month period. Nekken Forestry was slightly wetter than the Weather Station, while Mariculture was slightly drier.

Peleliu was somewhat drier than Koror. In January, Peleliu had 8.79 inches (82%), in February it had 17.96 inches (200%), and in March the island recorded 6.40 inches (97%)-a 3-month average of 11.05 inches per month or 126%. Overall, islands from Tobi in the south to Kayangel in the north were wetter than normal during the period.

We expect rainfall in Palau to be somewhat drier than normal into July, then about normal for the rest of the period through June 2001. While the La Niña is expected to keep the region between 3ºN and 10ºN wetter than normal for much of Micronesia through the spring, areas west of 150ºE will likely be somewhat drier than normal. The persistent eastward extension of the monsoon trough across the southern Philippines and into the Palau region may be delayed for 1-2 months, making rainfall values lower than normal. We expect the current La Niña to weaken by summer, bringing climatic conditions (e.g., monsoon activity) and rainfall patterns back to normal. Sub-surface ocean temperatures have warmed considerably over the last year in the western Pacific, setting the stage for another El Niño event. At this time, it is too early to tell when the onset of the next event will occur.

Tropical cyclone activity in the western North Pacific should return to normal by August, increasing the threat of a tropical cyclones from October through December for the Palau islands north of Angaur. Some tropical cyclone activity could occur in May if the monsoon surges into the Palau region.

Predicted rainfall for Palau from Apr 2000 through Jun 2001 is as follows:


Inclusive Period              % of long-term average
                    Koror and           Outer Atolls
                    Mountain Is.  S. of 8ºN    N. of 8ºN
Apr - Jun 2000         90%             90%         95%
Jul 2000 - Jun 2001   100%            100%        100%

- sources: UOG-WERI

Republic of the Marshall Islands: The RMI was much wetter than normal and much wetter than expected during the first 3 months of 2000. Southern islands were extremely wet with over 20 inches of rain in both January and February. We expect less rain, but still wetter than normal conditions through June. Rainfall is expected to return to normal by July. Tropical cyclone activity should return to normal in Micronesia by August, and developing tropical cyclones could affect the RMI from September to November.

Rainfall in the RMI was much heavier than anticipated in our last Newsletter. A persistent trade wind trough spent much of its time over and near the RMI, slightly farther east than during the same period of the 1998-1999 La Niña (see Table 1 and Figure 1). As a result, rainfall amounts and gradients in the RMI were extreme during the first three months of 2000. At Majuro (representative of southern atolls), January rainfall was 23.83 inches (283% of normal), February rainfall was 20.93 inches (340%), and that in March was 6.59 inches (80%). During the same period at Kwajalein (representative of central atolls at this time), January had 13.42 inches (294%), February had 8.13 inches (252%), and March had 3.87 inches (94%). The wettest area of the archipelago was Jaluit Atoll, which had a phenomenal 3-month total of 60.29 inches (280%). Ailinglapalap was drier with 23.95 inches (144%), while Wotje (representative of the northern atolls) had only 9.47 inches (88%). Farther north, Utirik was likely even drier. Farther west, Enewetok had above normal dry-season rainfall.

We expect the current La Niña to keep a fairly active trade wind trough near 5ºN from 170ºW to 150ºE. This should keep conditions in the southern RMI slightly wetter than normal until June, but much drier than in January and February. From July 2000 until June 2001, climatic conditions and rainfall patterns should return to normal. Since current western Pacific sub-surface ocean temperatures are much warmer than normal, there is a chance they could reach the surface, creating warmer SSTs. Thus, the RMI could see some strong westerly winds by late fall, producing heavier than predicted rains. However, it is too early to tell if this will occur.

As the La Niña wanes, tropical cyclone activity should become normal, but not before August. Wake Island and Enewetok could see typhoons in September and October. Developing tropical cyclones or tropical storms could affect the northern islands from September to November and the southern islands from mid-October to mid-December.

Predicted rainfall for the RMI from Apr 2000 through Jun 2001 is as follows:


Inclusive Period           % of long-term average
                                  RMI Atolls
                            Southern     Central   Northern 
Apr - Jun 2000                120%         105%       75%
Jul 2000 - Jun 2000           100%         100%      100%

- sources: UOG-WERI

Table 1. January-March 1999 (J-M 99) rainfall, January-March 2000 (J-M 00) rainfall, and the difference in 3-monthly rainfall (J-M 00 - J-M 99) for selected island locations in the western Pacific.


Location          J-M 00 Rainfall (in)  J-M 99 Rainfall (in)  (J-M 00 - J-M 99)
Pago Pago		  45.21			31.34		   +13.87
Guam (Tiyan)		  11.76			19.20		   -7.44
Anderson AFB, Guam	  14.36			20.57		   -6.21
Rota, CNMI		  14.46			17.84		   -3.38
Siapan IAP, CNMI	  6.59			11.96		   -5.37
Siapan Capitol Hill, CNMI 12.39			15.71		   -3.32
Tinian, CNMI		  9.67			16.72		   -7.05
Majuro, RMI		  51.35			21.20		   +30.15
Kwajalein		  25.42			10.21		   +15.21
Ailinglapalap, RMI	  23.95			18.49		   +5.46
Jaluit, RMI		  60.29			34.49		   +25.80
Wotje, RMI		  9.47			7.07		   +2.40
Korsae (SAWRS), FSM	  61.85			58.64		   +3.21
Pohnpei, FSM		  59.81			63.60		   -3.79
Nukuoro, Pohnpei State	  44.44			82.27		   -37.03
Pingalap, Pohnpei State	  65.66			64.93		   +0.73
Chuuk (Weno), FSM	  34.98			36.62		   -1.64
Lukunoch, Chuuk State	  44.93			53.09		   -8.16
Polowat, Chuuk State	  22.67			36.30		   -13.03
Yap, FSM		  18.90			20.59		   -1.69
Ulithi, Yap State	  17.59			19.65		   -2.06




APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 15 June 2000, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY of May 11 ,2000

SPECIAL SECTION - Markov model for Pacific SST and sea level


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 #331, 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 #331, 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 331
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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