In contrast to the reduction in SST anomalies during January and February, the Southern Oscillation Index or SOI has provided a continued indication of the ongoing strength of this El Niño event... Large negative values of -3.2 (January) and -2.7 (February) are the strongest yet seen for the 1997/98 event, reflecting the lower-than-normal atmospheric pressures near Tahiti and the higher-than-normal pressures near Darwin. Cyclones Tui, Ursula, Veli, and Wes affected areas from Samoa eastward in late January and early February. Weaker systems which did not develop to cyclones but did cause periods of heavy rain affected Tonga, Samoa, and the northern Cook Islands in early March. Tropical cyclone activity in Micronesia ended in December with Typhoon Paka , and further tropical cyclone activity is not likely until September or October.
SSTs are expected to cool slowly over the next few months, and then more rapidly as persistent low-level easterly winds develop along the equator from the coast of South America out toward the date line, accompanying a sharp rise in the SOI. The SST anomalies in the eastern Pacific will return to near normal or perhaps even drop below normal by the end of the year... Some climate models support cooling to normal SSTs in the eastern Pacific by then, while others support the development of La Niña (colder than normal) conditions. In either case, the strengthening easterly winds are expected to be a major influence on regional weather patterns in coming months.
Taken together, the SOI and SST conditions point toward a dry season for Micronesia that is both drier-than-normal and extended in length... Dry weather will continue to affect northern Micronesian islands into July, and southern Micronesian islands into June. For the Samoa region, a significantly drier-than-average rainy season and following dry season is also expected. See the following summaries for more details.
AMERICAN SAMOA: We are expecting very dry conditions for American Samoa. January rainfall was 10.64 inches or 85% of normal amounts, although nearly half of that rainfall was due to the close passage of Tui. February was very dry with only 2.02 inches or 16% of normal for the month. Record high temperatures also accompanied the dry spell in February. The heavy rains which caused flooding in Tonga in early March also brought substantial rain to Samoa, but there have been a considerable number of hot and dry days similar to the conditions in February. In the next month, the South Pacific Convergence Zone (SPCZ) will meander considerably, from the equator southward to 15°S latitude. Samoa will be near the western extent of the SPCZ, which will move eastward toward French Polynesia, leaving Samoa drier and with a reduced chance of getting a tropical cyclone. As a result, we have reduced the predicted March and April rainfall for the region to 30-40% of the average. Keep in mind that a direct or near-direct hit by a tropical cyclone would make the location very wet for a day or two and could make the month a wet one. After April, conditions will be very dry as trade winds strengthen over the region. This will extend the dry season and also make it significantly drier than normal. Significant wet weather is not expected to return until October. The rainfall observations and predictions for American Samoa and the surrounding region are:
Inclusive Period % of long-term average Samoa Region Jan 98 85% Feb 98 16% Mar-Apr 98 30-40% May-Sep 98 20-25% Oct-Dec 98 80% Jan-Mar 99 110%
GUAM/CNMI: We are expecting a record drought for Guam and the CNMI. January rainfall for Guam was 1.99 inches or 45% of normal values for the month. This rain came mostly from shearlines that transited the area. February rainfall at Guam International Airport was 1.22 inches or 31% of normal. Since the first of the year, there have been several hundred drought-related grass and forest fires on Guam, consuming thousands of acres of brush and forest areas. For January and February, Saipan International Airport had 1.00 inch (25% of normal) and 1.10 inches (37% of normal), respectively. Capitol Hill had 1.80 and 1.70 inches for January and February, respectively. Tinian was considerably wetter than the rest of the Mariana Islands in February, with some locations receiving up to 4.5 inches. Rota has been very dry over the last two months, with rainfall values less than 1 inch. Our rainfall predictions through March 1999 for Guam and the CNMI are as follows:
Inclusive Period % of long-term average Guam CNMI Jan 98 45% 25% Feb 98 31% 37% Mar-Jun 98 20% 20% Jul-Sep 98 60% 55% Oct-Dec 98 90% 90% Jan-Mar 99 100% 100%
MICRONESIA (FSM): We anticipate a record drought for all of the FSM, and we also anticipate that water resources will deplete a month earlier than during the 1983 drought. January and February rainfall for the FSM states was considerably less than the December amounts. All locations are expected to experience very dry conditions through May for the more equatorial islands and through June for the more northern islands. Water on many atolls is already becoming salty and surface water on the mountain islands is drying up. Chuuk and Pohnpei are reporting very dry conditions and are having many grass fires. Summaries for individual FSM states follow:
Chuuk: In January, Weno Island received only 1.25 inches or 12% of normal rainfall. Values were 0.31 inches (3% of normal) at Lukunoch and 1.12 inches (12% of normal) at Polowat. January rainfall at Namanuito Atoll and the Hall Islands has been revised, reducing it to only about 1.5 inches based on discussions with area residents. In February, Weno received 1.74 inches or 28% of normal. Lukunoch and Polowat had 1.64 and 1.42 inches, respectively, 20-25% of normal. Observations for March through the 19th of the month indicate very dry conditions at Weno, with only 0.13 inch recorded. The observed and predicted rainfall for Chuuk Lagoon and outer atolls is as follows:
Inclusive Period % of long-term average Chuuk Outer Atolls Lagoon Southern Northern Jan 98 12% 5-10% 25% Feb 98 28% 20-25% 20% Mar-Jun 98 15% 15% 15% Jul-Sep 98 70% 75% 60% Oct-Dec 98 90% 90% 85% Jan-Mar 99 100% 100% 100%
Pohnpei: Kolonia received only 0.64 inches or 5% of its normal rainfall in January. For the same month, Pingalap measured only 0.47 inches (4% of normal) and Nukuoro had 0.74 inches (5% of normal). February rainfall for Pohnpei was 1.98 inches (18% of normal), for Pingalap 1.15 inches (9% of normal), and for Nukuoro 2.12 (17% of normal). Conditions into March have remained very dry, with only 0.70 inch of rainfall recorded at Kolonia through the 19th of the month. Nukuoro had 1.02 inches and Pingelap had 0.93 inches for the same period. As a result of the low rainfall in Pohnpei, water rationing has been imposed in Kolonia, streams have already dried up, and rivers are already running at very low levels. The danger of high concentrations of water-borne diseases is very high, and all water should be boiled or chlorinated. The fire potential for Pohnpei is also very high. Water at many of the atolls could soon become salty. Rainfall observations and outlooks for Pohnpei State are as follows:
Inclusive Period % of long-term average Pohnpei Outer Atolls Island Eastern Southern Jan 98 5% 5% 5% Feb 98 18% 10% 15% Mar-May 98 10% 10% 10% Jun-Aug 98 50% 55% 60% Sep-Dec 98 85% 80% 85% Jan-Mar 99 100% 100% 100%
Kosrae: Rainfall at the Kosrae Airport during January was 1.29 inches or only 9% of normal. January values at Utwa, Tofol, and Tafunsak were between 1.28 and 1.17 inches (8-9%). In February, the airport received 1.67 inches (10% of normal), and Utwa and Tafunsak received 1.50 and 1.83 inches, respectively. There has been some more rainfall in March, with the airport recording 3.09 inches through the 19th, however conditions remain dry. As a result of the low rainfall in Kosrae, streamflow is expected to decrease rapidly, which will increase the danger of high concentrations of water-borne diseases. All water should be boiled or chlorinated. The fire potential for Kosrae may also become severe as with Pohnpei. The observed and anticipated rainfall for Kosrae is as follows:
Inclusive Period % of long-term average Kosrae Island Jan 98 9% Feb 98 10% Mar-May 98 10% Jun-Aug 98 65% Sep-Dec 98 90% Jan-Mar 99 100%
Yap: Like Guam and the CNMI, Yap had some January and February rainfall from passing shearlines. As a result, at the Yap airport, rainfall for January it was 4.45 inches or 61% of the average and for February it was 1.34 inches or 22%. At Ulithi and Woleai Atolls, January rainfall was 2.82 inches (40% of normal) and 3.26 inches (31% of normal), respectively. The February values for Ulithi and Woleai were not available, but based on satellite observations, the islands were considerably drier than during the previous month. Rainfall on Yap through March 19 has been very low, at only 0.09 inch. Conditions for the Yap State islands are expected to be much drier in March, April, and May, than in previous months. The reservoir on Yap is expected to dry up in March and will probably not receive significant rain until July. Observed and expected rainfall for Yap and its atolls is:
Inclusive Period % of long-term average Yap Outer Atolls: Island S.of 8°N N. of 8°N Jan 98 61% 30% 40% Feb 98 22% 25% 30% Mar-Jun 98 15% 20% 15% Jul-Sep 98 65% 75% 60% Oct-Dec 98 85% 90% 80% Jan-Mar 99 100% 100% 100%
MARSHALL ISLANDS (RMI) : We are expecting a record drought in the Marshall Islands. January rainfall at Majuro (representative of southern atolls) was only 1.57 inches or 19% of normal. Kwajalein (representative of northern atolls) and Ebeye received 0.66 inches or 8% of normal values. Other January rainfall for the Marshalls was 0.55 inches (5%) at Mili, 1.21 inches (12%) at Jaluit, and 1.43 inches (18%) at Wotje. February rainfall at Majuro was 0.34 inches (6% of normal), and at Kwajalein/Ebeye, rainfall was 0.91 (28% of normal). Similar conditions have extended in to March. Rainfall is expected to remain well below normal through May in the southern atolls and through June in the northern atolls. Water from wells on most of the atolls is expected to become brackish. The observed and anticipated rainfall amounts for the Marshall Islands are:
Inclusive Period % of long-term average RMI Atolls: Majuro & Srn Kwajalein & Nrn Jan 98 5-19% 8-18% Feb 98 5-10% 15-30% Mar-May 98 10% 10% Jun-Aug 98 70% 50% Sep-Dec 98 90% 80% Jan-Mar 99 100% 95%
PALAU: We are expecting a record drought in Palau. In January, rainfall at Koror was 4.72 inches or 44% of normal amounts, while 6.64 inches or 62% of normal amounts fell at Peleliu. We suspect that Kayangel has had less rain than Koror, while Tobi and Sonsorel have had slightly more rain than Koror. February rainfall at Koror was 2.40 inches (26% of normal) and that at Peleliu was 3.31 (about 33% of normal). Conditions are expected to be drier in March, April, and May. Surface water sources on Babelthab should be monitored closely as they could deplete quite rapidly. Brush fires could also be a problem on the larger islands. Observed and expected rainfall for Palau is as follows:
Inclusive Period % of long-term average Koror and Outer Atolls: Mountain Is. N. of 8°N S. of 8°N Jan 98 44-62% 40% 30% Feb 98 25-35% 25% 30% Mar-Jun 98 20% 15% 20% Jul-Sep 98 70% 65% 75% Oct-Dec 98 85% 80% 90% Jan-Mar 99 100% 100% 100%
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