Pacific ENSO Update - Special Bulletin, 1/26/98

Pacific ENSO Update - Special Bulletin
January 26, 1998

(update to Newsletter issued 4th Quarter 1997, Vol.3, No.4)

SPECIAL ISSUE BULLETIN

Due to the ongoing strong El Niño conditions affecting Micronesia and other areas of the tropical Pacific, this special bulletin is being issued with updated information to the last full issue of Pacific ENSO Update (4th Quarter, 1997). This limited distribution bulletin will be followed by the next full issue of Pacific ENSO Update for the 1st Quarter, 1998, to be issued in mid-February.

CURRENT CONDITIONS

There has been little change in eastern and central Pacific sea surface temperatures (SST) since the last issue of Pacific ENSO Update. SSTs remain well above normal in central and eastern equatorial areas. The Southern Oscillation Index (SOI) has risen instead of fallen as we anticipated, however this is primarily a result of lower than expected pressures over Darwin, Australia. The Australian monsoon became very active over northern and northeastern Australia, eastward to Samoa, creating Tropical Cyclones Ron, Susan, and Katrina. These cyclones affected areas from Vanauatu in the west to Tonga and the Cook Islands in the east. We had expected most activity to occur west of Australia and east of the date line, as was the case in December with Cyclone Pam. We still anticipate an eastward shift of tropical cyclone activity in the South Pacific. The most recent development of Tropical Cyclone Tui near Samoa is evidence of this.

In December, strong convective activity in the equatorial central Pacific led to the formation of twin cyclones, Typhoon Paka in the northern hemisphere and Cyclone Pam in the southern hemisphere. Paka eventually moved into the Marshall Islands, depositing substantial rain in the southern islands. It later intensified to a super typhoon, and on 16 and 17 December, it blasted Guam with 125 kt sustained winds, inflicting considerable damage to the island. The onset of the Australian monsoon created some weak northern hemisphere disturbances that dropped considerable rain on Koror and surrounding islands. Aside from the greater than normal December rainfall in Guam, the CNMI, and the southern Marshall Islands due to Typhoon Paka, and above normal rainfall in Palau due to some persistent tropical disturbances, the rest of Micronesia was dryer than normal. The stronger than expected Australian monsoon did kick off some equatorial disturbances that drifted into the sourthern Micronesia area. Further tropical cyclone activity in Micronesia is not likely until June or July, and then only in the western sections.

LOCAL VARIABILITY SUMMARIES

AMERICAN SAMOA: The Samoa region saw considerable activity as tropical disturbances and cyclones developed in the region, though most of this activity did not seriously affect the main islands. Cyclone Ron's severe impacts on Swains Island to the north, and the near miss of developing Tropical Cyclone Tui as it passed south of the main Samoan islands just recently are exceptions. December rainfall for Pago Pago was 7.84 inches or 54% of that normally expected. Our rainfall and cyclone activity predictions in the 4th Quarter 1997 Pacific ENSO Update are still valid, but may have to be modified to drier conditions if cyclone activity shifts east of the area before March.

GUAM/CNMI: December rainfall for Tiyan was 23.48 inches or more than 4 times the normal December rainfall. However, in only 2 days, Typhoon Paka dropped 21 of the 23.48 inches. Thus, without the typhoon, rainfall would have been about 50% of normal. We indicated in the last Pacific ENSO Update that the region would be wetter than normal if hit by a tropical cyclone and dryer than normal without a tropical cyclone. December rainfall for the Saipan International Airport was 5.30 inches, or 10 percent above normal. Typhoon Paka was also responsible for the excess rainfall at Saipan. Rota is estimated to have received 10-12 inches from Typhoon Paka. Our rainfall and cyclone activity predictions for January-December 1998 in the 4th Quarter 1997 Pacific ENSO Update are still valid.

MICRONESIA (FSM): Some islands nearer to the equator, such as Nukuoro, Lukunoch (and Palau to the west of FSM) received near or above normal December rainfall. This was primarily the result of small, northward moving tropical disturbances induced by the Australian monsoon. Our rainfall and tropical cyclone activity predictions in the 4th Quarter 1997 Pacific ENSO Update are still valid for 1998 for all of the FSM.

Chuuk: December rainfall for Weno Island was 2.88 inches or 27% of normal, while that at Lukunoch was a wet 11.51 inches or about 5% above normal. To the west at Polowat conditions continued to be extremely dry with 1% (one percent) of normal rainfall occurring in December. Since October, Polowat rainfall has only averaged 12% of normal, while that at Weno has only been 40% of normal.

Pohnpei: At Kolonia, December rainfall was 22% of normal, while rainfall for Pingalap and Nukuoro was about 30% and 68% of normal, respectively. As a result of the low rainfall in Pohnpei, streamflow is expected to decrease, increasing the danger of high concentrations of water-borne diseases. The fire potential for Pohnpei will also be high.

Kosrae: Rainfall at the Kosrae Airport for December was 8.61 inches or 59% of normal, while that for the same period at Utwa was 11.33 inches or about 75% of normal. As a result of the low rainfall in Kosrae, streamflow is expected to start decreasing, which will increase the danger of high concentrations of water-borne diseases. The fire potential for Kosrae will also increase.

Yap: Rainfall for December was 5.93 inches or 66% of the average at the Yap airport. At Ulithi, 3.94 inches fell or about 50% of norma, while at Woleai Atoll, December rainfall was 3.35 inches or 29% of normal. The reservoir on Yap is not expected to receive significant rain until July.

MARSHALL ISLANDS (RMI) : At Majuro (representative of the southern atolls), rainfall for December was 7.63 inches or 64% of normal. About 5 inches was primarily the result of Typhoon Paka. Without Paka, rainfall would have been about 22% of normal. At Kwajalein (representative of northern atolls), December rainfall was 5.03 inches or 63% of normal values. Paka dropped 3.59 inches of that in 2 days. Without Paka, values would have been about 18% of normal. From 14 December to 13 January, Kwajalein received only 0.35 inches of rain. Our rainfall and cyclone activity predictions in the 4th Quarter 1997 Pacific ENSO Update are still valid for 1998 for all of the Marshall Islands, except that further tropical cyclone activity is unlikely until at least late 1998 and probably not until the fall of 1999.

PALAU: At Koror, rainfall totals were above normal for the first time since March. At the Koror weather station, December rainfall was 11.35 inches or 6% above normal. Farther south at Peleliu, values were 30% above normal values. Our rainfall and cyclone activity predictions in the 4th Quarter 1997 Pacific ENSO Update are still valid for 1998 for the Republic of Palau.

ACKNOWLEDGEMENTS and FURTHER INFORMATION

The information in this special bulletin was prepared by WERI and PEAC. For more information, please contact:

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.

PACIFIC EL NINO-SOUTHERN OSCILLATION (ENSO) APPLICATIONS CENTER:
HIG #331, 2525 Correa Road, Honolulu, Hawaii 96822
Contact R. Tanabe at 808-956-7110 for more information on ENSO-related climate data for the Pacific Islands.
Contact A. Hilton at 808-956-2324 for more information on Pacific ENSO Update and applications.

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.