Pacific ENSO Update

1st Quarter 2000 - Vol. 6 No. 1


CURRENT CONDITIONS


SST

December equatorial SST anomalies in the Central and Eastern Pacific [Niño 3.4 region (170W-120W)] were -1.5ºC (-2.7ºF), corresponding to a weak-moderate La Niña event. This is the second year of La Niña conditions, but this event is expected to be weaker than the moderate-strong La Niña of 1998-1999. Wet weather and drought conditions associated with La Niña should not be as extreme as during the 1998-99 event. However, 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 June-July timeframe. Much of Micronesia between 3ºN and 10ºN will be somewhat wetter than normal for the first half of the year, but not as wet as during the first five months of 1999. We expect conditions to return to normal by the boreal fall.

SST anomalies in the Central and Eastern equatorial Pacific (Niño 3.4 region (170W-120W) reached -1.5ºC (2.7ºF) in December. Despite its persistence, the area of lower than normal equatorial SST has remained narrow. Radar images from the TOPEX-Poseidon Satellite indicate that sub-surface ocean temperature anomalies that stabilized in summer with some areas greater than -2°C (-3.6ºF), have now cooled to -6ºC (-10.8°F) and have expanded dramatically. This provides some support for cooler SSTs and an intensifying La Niña. However, the radar also indicates that sub-surface ocean temperatures have warmed considerably in the Western Pacific, and in fact, have started to push into the Central Pacific. These sub-surface temperatures were +4ºC (+7.2ºF) at a depth of 150 meters near 170ºE. Conditions are setting up for another El Niño event, but it is much too early tell whether this will occur in 2001 or later. In November, most climate models predicted a continuation of La Niña conditions into theboreal fall and winter of 2000. However, in December, there was large disagreement among the models. Some are predicting a continuation of weak La Niña conditions into the boreal fall and winter of 2000. Others are pointing to neutral conditions by the boreal fall. And, two models, the canonical correlation analysis model and the Markov model (Figure 1), are even predicting a movement to weak warm conditions. This change in the model behavior may be due to the very large difference between East Pacific and West Pacific sub-surface equatorial ocean temperatures, as seen in the anomalies. Our predictions are leaning toward continued weak to moderate La Niña conditions until April, then weak conditions into the boreal summer, and near normal values by the boreal fall. The "La Niña" conditions have been sufficient to maintain the characteristic cold tongue and cloud minima along the equatorial belt from 150ºW to 150ºE. This has kept rainfall amounts much below normal in the equatorial regions east of 150ºE and in the Southern Hemisphere north of 10ºS and east of 170ºE. The large changes in computer model SST predictions between December and earlier months cautions us to be prepared for the onset of another El Niño as early as 2001.

SOI

The SOI continued to hover between +0.5 and +1.5 during the past 5 months, suggesting a weak to moderate La Niña event. This positive SOI has been consistent with observed rainfall patterns in the equatorial Central and Western Pacific, east of 150ºE. Low-level equatorial easterly winds have been nearly 5 knots (3 m/s) stronger than normal, a condition consistent with reduced rainfall across the belt. 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 stubbornly remaining along the equator, reduced evaporation coupled with strong subsidence will likely make conditions drier than normal in equatorial regions. Rainfall in other parts of Micronesia and in American Samoa will be closer to normal.

The December 1999 Southern Oscillation Index (SOI) value of +1.5 standard deviations above normal was the highest value since April 1999. SOI values hovered between +0.9 in September to the +1.5 in December, and as of mid February, the value was +1.0. The positive SOI is in phase with the negative Central Pacific SSTs, and is consistent with observed rainfall patterns. The equatorial SOI between the Eastern Pacific and Indonesia also remains 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.

While, trade winds have been stronger than normal, the trade wind trough in eastern Micronesia has not been particularly persistent. However, even the sporadic development of disturbances in the trough have kept rainfall values near normal between 4ºN and 10ºN in the western North Pacific. Shear lines (washed out cold fronts) in the western North Pacific have also been weaker and less frequent than expected. This has restricted most of the rainfall south of 10ºN, keeping conditions in the Mariana Islands, in the northern Marshall Islands, and at northern Yap Islands somewhat drier than expected. Most Micronesian Islands between 4ºN and 10ºN will have near normal to slightly above normal rainfall into June. The northern Marshalls will likely have below normal rainfall, especially from Wotje, northward. Near equatorial islands south of 4ºN and east of 160ºE will be considerably drier than normal, although conditions should improve by April or May.

In the Southern Hemisphere, the east-west oriented portion of the South Pacific Convergence Zone (SPCZ) has been established across 10ºS in an off and on manner (Figure 3), and monsoon activity across Australia and into the Southwest Pacific has been relatively weak to date. This has delayed tropical cyclone development in the region. The north-south oriented portion of the SPCZ has been anchored near 150ºW, but has also been highly variable in its organization. The position and intensity of the SPCZ will likely keep rainfall in the Samoa region near normal to slightly above normal. Month-to-month rainfall will be variable, fluctuating with the position of the SPCZ.

Over 1999, most Micronesian islands had near normal rainfall. However, the La Niña had its impact on the 1999 rainfall distribution. Table 1 summarizes the amount and percent of normal of 1999 rainfall for selected Micronesian Islands and for Pago Pago, American Samoa.

TROPICAL CYCLONE ACTIVITY

Tropical cyclone (TC) activity was below normal in the western North Pacific. There were 34 numbered TCs in 1999 (versus an average of 38), but most of these were weaker and smaller than normal. In fact, there were only 24 named storms (4 less than the average): 13 tropical storms and 11 typhoons (6 less than the average) (Source: JTWC, Pearl Harbor, HI). Most of the 1999 TCs formed west of 135ºE, characteristic of La Niña periods. The average location of development was near 130ºE, the farthest west the average development location has been since 1973. Only one super typhoon-Super Typhoon Bart in September-developed in 1999, three less than the long-term average number. Stronger than normal trade winds, subdued monsoon activity, and a poorly developed near-equatorial trough all contributed to the low output of strong tropical cyclones and to the far-western average longitude of development. Tropical cyclone activity could resume as early as April or May in the Northwest Pacific, if the La Niña conditions weaken substantially before this period. If the La Niña remains moderate or even weak into the boreal summer, then tropical cyclone activity for Micronesia will not likely recur until September 2000. Southern Hemisphere significant tropical cyclone activity will likely remain west of the International Date Line. Thus, American Samoa and islands east of the Date Line should not experience significant tropical cyclone activity until the next El Niño event.

As oceanic and atmospheric conditions return to normal, our skill at predicting rainfall for specific regions will decrease. Rainfall will return to "normal", with high values of month-to-month variability. We will vigilantly monitor conditions as they set up for the next El Niño. January 2000 rainfall values are not included in this update, but fit well with the following predictions.


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:January 2000 looked more like July with trade winds prevailing 90 percent of the time. However, rainfall totals, especially for sites on the windward sides of the islands, were anything but "summer-like". Three shear lines (16, 18-20, and 26 January) and three upper level troughs (3, 12, and 19-20 January) helped provide the forcing to enhance shower activity. Two of the upper level troughs, on 3 and 12 January, brought enough instability to produce thunderstorms and minor flooding over portions of the island of Hawai'i.

While the persistent trades brought ample rainfall to the windward areas, the leeward sides, as expected in this type of weather pattern, generally saw below normal rainfall. The agriculture sector has been counting on more rainfall for relief from the abnormally dry conditions that have plagued these areas for about three years.

Kevin Kodama - Senior Service Hydrologist, NWSFO Honolulu, HI

For a more complete summary, and the county by county wrap-ups, please see the January 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 to slightly above normal. 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. Some weak tropical cyclones could develop in the monsoon trough to the north of the islands.

Rainfall in the Samoa region was slightly below normal from October-December 1999 as anticipated in our last Newsletter. At Pago Pago International Airport, October rainfall was 8.72 inches (83%), November rainfall was 10.54 inches (97%), and that in December was 12.50 inches (86%). For the quarter, rainfall averaged 88% of normal. The north-south oriented portion of the South Pacific Convergence Zone (SPCZ) has remained anchored near 160°W (Figure 3), but has fluctuated in intensity. This has brought periods of heavy rainfall and periods of relatively dry weather to the Samoa region. It is probable that the stronger than normal subsidence over the region is associated with the current La Niña, and its westward deflection of the monsoon trough. This has weakened the east-west oriented portion of the SPCZ, keeping conditions drier than normal in the northern Cook Islands, the Samoas, Tokelau, and Tuvalu. While some computer models indicate the continuation of La Niña conditions into late 2000, we expect atmospheric conditions to moderate with a return to near normal conditions by the September-October timeframe. Also, sub-surface ocean temperatures continue to increase in the western Pacific setting the stage for the next El Niño, but not beforethe spring of 2001.

A few developing tropical cyclones may affect the Samoas, but strong tropical storm-force or hurricane-force winds are not expected until the next El Niño.

Predicted rainfall for American Samoa from Jan 2000 through Mar 2001 is as follows:


Inclusive Period         % of long-term average
                              Samoa Region
Jan - Jun 2000                     95%
Jul - Mar 2001                    100%

- sources: UOG-WERI and PEAC

Guam/CNMI: After a dry October-January, rainfall for Guam and the CNMI is expected to be normal to slightly above normal from February until June. Afterward, we expect rainfall to return to normal with large month-to-month variability. Tropical cyclone and monsoon activity are expected to return to normal, at least by August. This will contribute to high month-to-month variability in the rainfall, but normal to slightly above normal rainfall from July to October.

The end-of-year rainfall at Guam International Airport (Tiyan) was much drier than normal. In October, the Airport received 7.98 inches (66%), in November 5.42 inches (66%), and in December 3.51 inches (65%). For the three months, rainfall averaged only 66%. Despite these very dry three months, the 1999 rainfall totaled 86.87 inches, or 95% of normal rainfall. At Andersen Air Force Base (AAFB), October rainfall was 8.96 inches (70%), November rainfall was 8.60 inches (95%), and December rainfall was 4.79 inches (80%). For the 3-month period, rainfall averaged 80%. The 1999 rainfall for the Air Force Base was 96.02 inches or 98% of normal.

Saipan was even drier than Guam during the last quarter of the year. At Saipan International Airport (SIA), October rainfall was 6.24 inches (58%), November rainfall was 4.27 inches (74%), and December rainfall was 2.32 inches (60%). This gave a 3-month average of 64%. Even with this dry period, 1999 rainfall totaled 68.15 inches or 92% of normal. As is normal, Capitol Hill was wetter. There, October rain amounted to 9.47 inches (79%), November rain measured 4.80 inches (66%), and December rain totaled 4.39 inches (91%). This created a 3-month average of 79%, but for all of 1999, Capitol Hill had 82.27 inches or 99%.

As expected, rainfall at Rota International Airport was similar to Guam's, while that at Tinian International Airport was similar to Saipan's. At Rota, October rainfall was 8.95 inches (71%), November rainfall was 6.61 inches (77%), and that for December was 3.89 inches (68%). For the three months, the average was 72%. The NASA rain gauges at the Rota Resort and Country Club indicated that northern Rota was drier with 7.89, 3.70, and 2.89 inches for the respective months-about 75% of that at the Airport. For 1999, Rota's rainfall was 92.03 inches or 97%. At Tinian, rainfall was 7.92, 3.89, and 4.28 inches for the respective months, giving a 3-month average of about 70%. For the year, Tinian had 71.59 inches or 93% of normal.

We expect the Mariana Island to have slightly above normal rainfall from February-June as a result of the current La Niña. However, a more rapid disappearance of the event will make rainfall more normal. To date, the trade wind trough over southeastern Micronesia has been weaker than expected and shear lines affecting the Mariana Islands have been less frequent than expected, making January drier than anticipated (Figure 3).

At this point, we expect tropical cyclone activity to return to normal by August. If the La Niña weakens rapidly, the region could see tropical cyclone development in the region of Chuuk in May. These cyclones could threaten the southern Marianas.

Predicted rainfall for the Mariana Islands from Jan 2000 through Mar 2001 is as follows:


Inclusive Period         % of long-term average
                      Guam/Rota       Saipan/Tinian
Jan - Jun 2000          105%              105%
Jul 2000 - Mar 2001     100%              100%

- sources: UOG-WERI

Yap State: After a wetter than normal 1999, Yap State is expected to have rainfall closer to normal. The La Niña will make the first 5-6 months of the year slightly wetter than normal. Tropical cyclone activity is expected to be back to normal by August.

Rainfall at Yap Airport during October, November, and December was 4.95 inches (41%), 12.95 inches (143%) and 12.47 inches (139%), respectively. This made the last quarter of the year 108% of normal. For all of 1999, Yap had 116% of normal rainfall. Gilman was wetter, Luweech was about the same, and other areas of the island were drier than the Airport. At Ulithi, October had 6.85 inches (67%), November had 15.87 inches (206%), and December had 13.12 inches (172%)-very wet, averaging 148%. For the entire year, Ulithi had 112.30 inches or 110% of its normal rainfall. Farther south at Woleai Atoll, rainfall was 7.46 inches (55%), 16.88 inches (156%), and 13.93 inches (122%) for the last three respective months of the year-111% of normal. The year was wet for Woleai-173.74 inches or 125% of normal.

We expect conditions to be somewhat wetter than normal for all of Yap State, but especially for southern portions in response to tropical disturbances that develop in the trade wind trough to the east and move through the region. Yap will see less disturbances than southern areas, but will get some additional rain from shear lines (Figure 3). The monsoon could also be active into November, bringing several episodes of heavy rainfall. Tropical cyclone activity should return to normal by August, but could return to normal as early as May if the La Niña weakens more rapidly than anticipated. Greatest threats for Yap State will be from October-December.

Predicted rainfall for Yap State from Jan 2000 through Mar 2001 is as follows:


Inclusive Period                % of long-term average
                             Yap               Outer Atolls:
                            Island       S.of 8·N     N. of 8·N
Jan - Jun 2000               105%          115%         110%
Jul 2000 - Mar 2001          100%          100%         100%

- sources: UOG-WERI

Chuuk State: After a wetter than normal 1999, Chuuk State is expected to remain wetter than normal until June. 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. Some tropical cyclone activity could affect Chuuk State as early as May, if the La Niña weakens faster than expected.

Like Yap State, Chuuk State was wetter than normal in 1999, primarily as a result of the La Niña-induced wet boreal spring-especially March and April. The continuation of La Niña conditions will also make the 2000 spring wet as has been the case in November and December, but not as wet as in 1999. During the last three months of 1999, Chuuk Airport had 12.26 inches (91%) of rain in October, 13.00 inches (126%) in November, and 19.58 inches (181%) in December. This is a 3-month average of 133%. For the year, Chuuk had 154.78 inches or 115%. At Lukunoch, the year was even wetter with 174.25 inches or 130% of normal. The island had 12.42 inches (93%) of rain in October, 11.16 inches (108%) in November, and 15.68 inches (145%) in December-a 3-month average of 115%. Polowat was somewhat drier than the rest of Chuuk State, and would have been considerably drier than the remainder of the region had it not been for a very wet March (20.22 in) and April (31.41 in). Several days of rainfall were missing from the October and November records at Polowat. Given the proximity to Chuuk, Polowat likely had at least 50% of Chuuk's rainfall. This would give Polowat about 20.45 inches (68%) for the three months and 123.96 inches or 103% for the year.

The current La Niña is expected to keep the region between 3ºN and 10ºN wetter than normal through spring due to disturbances that develop in the trade wind trough (Figure 3), but not as wet as in the winter and spring of 1999. There are some indications that the La Niña is weakening and that could cause conditions to become drier. Also, a very active Southern Hemisphere monsoon trough could make low level winds more northeasterly over Chuuk State, reducing rainfall there. Rainfall should return to normal by July. The monsoon could be active into November, bringing several episodes of heavy rainfall. Tropical cyclone activity should be back to normal by August, and could affect Chuuk State from October-December. If the La Niña weakens rapidly, Chuuk State could see tropical cyclones in May.

Predicted rainfall for Chuuk State from Jan 2000 through Mar 2001 is as follows:


Inclusive Period               % of long-term average
                        Chuuk         Outer Atolls
                        Lagoon    Southern    Western
Jan - Jun 2000          115%       120%        105%
Jul - Mar 2001          100%       100%        100%

- sources: UOG-WERI

Pohnpei State: Rainfall during 1999 was mixed in Pohnpei State, being extremely wet at Nukuoro to near normal on Pohnpei. Pohnpei State is expected to be wetter than normal through the boreal spring due to the ongoing La Niña, then will have rainfall amounts closer to normal for the remainder of the period. Tropical cyclone activity 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 set up.

Despite the 1999 La Niña, rainfall on Pohnpei Island was not as heavy as at other locations in the State. At the Pohnpei weather station, 1999 rainfall was 194.65 inches or 103% of normal. During the last three months of the year, the weather station measured 10.99 inches (66%) in October, 13.33 inches (85%) in November, and 25.89 inches (170%) in December-107% for the period. Other parts of the island were drier with most other parts of the island experiencing about 90-95% of normal rainfall for 1999.

The center of the heavy-rain disturbances that moved across Micronesia from January through April 1999, moved just south of Pohnpei Island, on a track across Kosrae, Pingalap and Nukuoro. As a result, Pingalap was considerably wetter than Pohnpei Island with 220.33 inches (124%) for the year. In October, Pingalap had 15.56 inches (105%), in November it had 17.37 inches (122%), and in December the island saw 17.58 inches (131%). This amounted to an average of 119% for the quarter. Nukuoro was even wetter with 225.06 inches or 151% of normal rainfall for the year. However, during the last three months, the atoll was considerably drier with 10.81 inches (101%) in October, 6.74 inches (56%) in November, and 13.59 inches in December (113%). The quarterly average was only 90% of normal.

After a dry 1998 and a dry January-March 1999, Kapingamarangi saw relief from April-August. However, the resurgence of La Niña brought very dry conditions back to near equatorial areas of the western Pacific. Rainfall measurements on the island are only available from April, but it is likely that the annual rainfall was only about 73 inches or 66 percent of normal. The last three months were very dry with 3.16 inches (66%) in October, 2.79 inches (34%) in November, and 2.66 (30%) in December-43% for the quarter.

The current La Niña is expected to keep the region between 3ºN and 10ºN wetter than normal through the spring due to disturbances that develop in the trade wind trough (Figure 3), but not as wet as in the winter and spring of 1999. Equatorial areas east of 160ºE will be considerably drier than normal. By July, rainfall 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 onset of the next El Niño event. Since current western Pacific sub-surface ocean temperatures are warming so rapidly, 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. It is too early to tell with certainty at this point.

Predicted rainfall for Pohnpei State from Jan 2000 through Mar 2001 is as follows:


Inclusive Period          % of long-term average
                     Pohnpei           Outer Atolls:
                     Island    Eastern    Southern    Equatorial
Jan - Jun 2000        110%      120%        120%         60%
Jul - Mar 2001        100%      100%        100%        100%

- sources: UOG-WERI

Kosrae: During 1999, rainfall on Kosrae was slightly wetter than normal. Kosrae State is expected to be wetter than normal through the boreal spring due to the ongoing La Niña, then will have rainfall amounts closer to normal for the remainder of the period. Tropical cyclone activity is expected to be back to normal by August, but significant tropical cyclones will not likely threaten Kosrae State until the next El Niño onset.

In 1999, Kosrae Airport had 214.51 inches of rain or 104% of normal. Utwa had 225.92 inches (110%), Tofol had 209.38 inches (102%), and Tafunsak had 205.03 inches (99%). January, April, and December were all exceptionally wet, reflecting the influence of La Niña. This was primarily due to disturbances that developed in the trade wind trough to the east and tracked just north of and over Kosrae. At the Airport, rainfall for October was 12.09 inches (75%), for November was 17.95 (113%), and for December was 24.09 (166%). This amounts to an average of 101% for the last quarter of the year. Tofol and Tafunsak were drier than the Airport while Utwa was wetter.

We expect Kosrae to have slightly wetter than normal rainfall until June in response to the current La Niña. La Niña is expected to keep the region between 3ºN and 10ºN wetter than normal through the spring due to disturbances that develop in the trade wind trough (Figure 3), but not as wet as in the winter and spring of 1999. Afterwards, rainfall should return to near normal values from July 2000 through March 2001. Tropical cyclone activity should not pose a direct threat to Kosrae until the next El Niño begins. Since current western Pacific sub-surface ocean temperatures are warming so rapidly, there is a chance that Kosrae could see some strong westerly winds by late fall, producing heavier than predicted rains. However, it is too early to tell at this point.

Predicted rainfall for Kosrae State from Jan 2000 through Mar 2001 is as follows:


Inclusive Period     % of long-term average
Jan - Jun 2000                 110%
Jul 2000 - Mar 2001            100%

- sources: UOG-WERI

Republic of Palau: The Republic of Palau had well above normal rainfall during 1999, but less than normal rainfall during the last three months. We expect the first half of 2000 to be slightly wetter than normal for the Island Nation. By July, rainfall amounts should return to normal. Tropical cyclone activity could threaten islands north of Angaur from October through December.

The Koror Weather Station experienced October rainfall of 5.88 inches (42%), November rainfall of 9.51 (84%), and December rainfall of 16.37 (137%)-an average of 88% for the three months. For the year, the Weather Station at Koror measured 171.89 inches or 119% of normal. Nekken Forestry had 187.02 inches (126%) for the year, while Mariculture had 177.60 inches (120%).

Peleliu's annual rainfall was similar to that on Koror with 176.09 inches (119%). However, Peleliu was wetter during the last three months with 13.31 inches (96%) in October, 11.30 inches (100%) in November, and 14.06 inches (118%) in December-a 105% average. Overall, islands from Tobi in the south to Kayangel in the north were wetter than normal in 1999.

We expect rainfall in Palau to be somewhat wetter than normal into June, then about normal for the rest of the period through March 2001. La Niña is expected to keep the region between 3ºN and 10ºN wetter than normal through the spring due to disturbances that develop in the trade wind trough (Figure 3), but not as wet as in the winter and spring of 1999. Some eastward extent of the monsoon trough across the southern Philippines and into the Palau region will also make rainfall values high. 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 are warming considerably in the western Pacific, setting the stage for another El Niño event. It is too early to tell when the onset of the next event will occur. For Palau, tropical cyclone activity should return to normal by August, increasing the threat of a tropical cyclones from October through December for the islands north of Angaur.

Predicted rainfall for Palau from Jan 2000 through Mar 2001 is as follows:


Inclusive Period              % of long-term average
                    Koror and           Outer Atolls
                    Babelthaup     S. of 8ºN    N. of 8ºN
Jan - Jun 2000        115%            120%        110%
Jun2000 - Mar 2001    100%            100%        100%

- sources: UOG-WERI

Republic of the Marshall Islands: Overall, the RMI was drier than normal during 1999. While southern islands were near normal to slightly wetter than normal, the northern islands were drier than normal. We expect these rainfall trends to continue for the first half of 2000, with movement toward normal rainfall by July. Tropical cyclone activity should return to normal by August, and developing tropical cyclones could affect the RMI from September to November.

Rainfall during 1999 was near normal in the south and drier than normal in the north. At Majuro (representative of southern atolls), rainfall was 128.17 inches or 98% of normal, and that at Kwajalein (representative of northern atolls) was 86.36 (85%) of normal. The wettest area was Jaluit Atoll with 155.75 (119%), while Wotje had only 62.38 inches (64%) and Utirik was likely even drier.

Rainfall for the last three months of the year in the northern RMI was not as heavy as anticipated in our last Newsletter. A persistent upper level trough hung across the northern RMI much of the time, bringing extended periods of dry weather. However, in the south, the trade wind trough spent much of its time over and near the RMI. During the last three months of 1999, rainfall at Majuro was 17.85 inches (129%) for October, 17.27 inches (135%) for November, and 9.85 inches (83%) for December-a 3-month average of 116%. At Kwajalein, rainfall for the respective three months was 11.95 (100%), 10.95 (103%), and 6.77 (84%)-an average of 96%. The more southern islands were wetter and the more northern islands drier.

We expect the current La Niña to keep a fairly active trade wind trough near 5ºN from 170ºW to 150ºE (Figure 3). This should keep conditions in the southern RMI slightly wetter than normal until June. An upper level trough overlying a large area of high pressure should keep the northern RMI drier than normal until June. Some disturbances from the trade wind trough of the trough itself could drift over Kwajalein, providing periods of heavy rain as occurred in January. In fact, Kwajalein had its second wettest January in history. From July 2000 until March 2001, climatic conditions and rainfall patterns should return to normal. Since current western Pacific sub-surface ocean temperatures are warming so rapidly, there is a chance the RMI could see some strong westerly winds by late fall, producing heavier than predicted rains. However, it is too early to tell with certainty at this point.

As the La Niña wanes, tropical cyclone activity should become normal. This means that Wake Island 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 Jan 2000 through Mar 2001 is as follows:


Inclusive Period           % of long-term average
                                  RMI Atolls
                            Southern     Northern
Jan - Jun 2000                110%          90%
Jul 2000 - Mar 2000           100%         100%

- sources: UOG-WERI

Table 1. Annual rainfall amounts (inches) and percent of normal annual rainfall for 1999 at selected Micronesian Islands and for Pago Pago, American Samoa.


Location                           1999 Rainfall (in)      % of Normal
Pago Pago, American Samoa               126.79                104
Andersen Air Force Base, Guam            96.02                 98
Guam International Airport, Guam         86.87                 95
Saipan International Airport, CNMI       68.15                 92
Capitol Hill, Saipan, CNMI               82.27                 99
Tinian International Airport, CNMI       71.59                 93
Rota International Airport, CNMI         92.03                 97
Yap WSO, Yap, FSM                       138.71                116
Ulithi, Yap, FSM                        112.30                110
Woleai, Yap, FSM                        173.74                125
Chuuk WSO (Weno Is), FSM                154.78                115
Polowat, Chuuk, FSM                     117.96                 98
Lukunoch, Chuuk, FSM                    174.25                130
Pohnpei WSO, Pohnpei, FSM               194.65                103
Palikir, Pohnpei, FSM                   172.29                 91 (of WSO value)
Nukuoro, Pohnpei, FSM                   225.06                151
Pingalap, Pohnpei, FSM                  220.33                124
Kapingamarangi, Pohnpei, FSM             65.46 (Apr-Dec)       87 (Apr-Dec)
Kosrae, SA WRS, Kosrae, FSM             214.51                104
Utwa, Kosrae, FSM                       225.92                110
Koror WSO, Palau                        171.89                116
Peleliu, Palau                          176.09                119
Majuro WSO, RMI                         128.17                 98
Jaluit, RMI                             155.75                119
Kwajalein, RMI                           86.36                 85
Wotje, RMI                               62.38                 64




APPENDICES:

Long-Lead Outlook for Hawaiian Islands issue dated 17 February 2000, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY of February 14 ,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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