Pacific ENSO Update

3rd Quarter 1998 - Vol.4 No.3


The current El Niño, which has been the most intense on record, continues to wind down. Considerable cooling of eastern and ventral equatorial Pacific sea surface temperatures (SST) has occurred. There also has been a large reduction in the size of the area covered by the warmer than normal ocean temperatures.. In December and January, the SST anomalies in the eastern equatorial Pacific peaked at over 9ºF (5ºC) warmer than normal. In April, the anomalies had fallen to about 5ºF (3.3ºC), and by the end of August, they had fallen to a small, shallow area of 1-2ºF (1ºC) in the extreme eastern equatorial Pacific. A small area of the equatorial central Pacific showed anomalies up to -2.0ºC (-3.6ºF) colder than normal from 160ºW to 120ºW. Virtually all statistical-dynamic climate models and dynamic climate models are now predicting colder than normal equatorial sea surface temperatures by the October time frame, leading toward a La Niña (cold event) scenario.

The area of below normal sea level heights that was prominent over Micronesia during much of 1997, has moved to the southeast, and in May extended from 150ºE to 120ºW, on the southern side of the equator. With a La Niña developing, we expect lower than normal sea level heights to migrate to the equatorial Central Pacific. From January to March, the Southern Oscillation Index (SOI) averaged more than -3 units below normal. the SOI began to rise in May, and became slightly positive by July. Equatorial easterly winds and trade winds then strengthened, reinforcing dry conditions over equatorial Micronesia and American Samoa.

Tropical cyclone activity in the western North Pacific during the first half of 1998 has been even quieter than anticipated. No tropical storms or typhoons had developed in the western North Pacific until Typhoon Otto developed northwest of Yap in early August. since the first of September, there had been only five named tropical cyclones in the western North Pacific. Tropical cyclone activity is not likely to threaten Micronesian islands until September or October. We expect to see several straight moving tropical cyclones move through western Micronesia from October through early to mid December. La Niña (cold event) conditions will likely restrict early 1999 tropical cyclone activity to areas west of Micronesia. In the southern hemisphere, tropical cyclone activity will shift to regions west of the date line, and American Samoa will not likely experience tropical cyclones during the remainder of 1998 or in 1999.


SPaRCE: Connecting Science with Education

In the last issue of the Pacific ENSO Update, we introduced you to the Environmental Verification and Analysis Center (EVAC), located in Norman, Oklahoma. EVAC is comprised of various research projects including the Schools of the Pacific Rainfall Climate Experiment (SPaRCE).

The Schools of the Pacific Rainfall Climate Experiment (SPaRCE) is a cooperative field project involving over 170 schools from various Pacific island and atoll nations. Students and teachers from elementary school, middle school, high school, college, and trade school participate in collecting and analyzing a unique set of environmental measurements. Other collaborators include the Meteorological Services in Majuro, Pohnpei, Western Samoa, Papua New Guinea, Tonga, Niue, and the Solomon Islands; PEACESAT Hawaii; the Pacific Resources for Education and Learning; the South Pacific Regional Environmental Programme; University of Hawaii Sea Grant Extension program; the College of Micronesia; the U.S. Department of Energy's Tropical Western Pacific Atmospheric Radiation Measurements project; Flinders University in Adelaid, Australia; and the Australian Meteorological and Oceanographic Society. Please take the time to find out more about SPaRCE.

The Perils of Modern Technology

We have had to relocate the PEAC website to the new address This is due to the fact that the current host machine (naulu) has been repeatedly "hacked" and constitutes a threat to the security of the entire School of Ocean and Earth Science and Technology network. Since naulu is aging, we will be replacing it with new equipment in the coming months. The old address ( still works, but now points to the University of Hawaii, Department of Meteorology's Internet weather server. I link to the new PEAC site is located at the top of that page. We are sorry for any incoveniences this may cause.

NOTE: A number of personnel changes have impacted the operations of the Pacific ENSO Applications Center. Our original applications scientist (Y-P Yu aka Chip) resigned and moved to San Diego in 1997 then this spring Alan Hilton (the anchor of the Update publication) was called to sea by NOAA_ We have added a Research Assistant (Raymond Tanabe) and a Part-time Research Associate (Cheryl Anderson). We have benefited immensely from the voluntary assistance of EVAC at the University of Oklahoma headed by Dr. Mark Morrissey whose ties to the Pacific date back to his time as a student at the University of Hawaii. Please accept our apologies for any stumbles as we adapt to our new publication process.

Thomas A. Schroeder
Joint Institute for Marine and Atmospheric Research

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.

The consensus of current model predictions indicate that a cooling trend in the sea surface temperatures (SSTs) is likely over the coming months. There is less of a consensus, however, on the extent of this cooling. The predicted cooling trend in SSTs, which is noticeably stronger that in previous forecasts, suggests the current El Nino ending between now and September and the development of a cold event by the end of the year. The LOCAL VARIABILITY SUMMARIES in the following section provide the outlooks based on this forecast.


Information in the LOCAL VARIABILITY SUMMARIES section is based on an expectation that SST's will continue to cool over the coming months. Any changes in trends, and their impact on these outlooks, will be reported in future issues of the Pacific ENSO Update. As noted in each issue, the following summaries of expected local climate variability for the various island areas indicated are not based on official forecasts (unless otherwise stated). Further information is available from your local National Weather Service office, or from the sources listed in the acknowledgements section.

Hawaii:Rainfall amounts were generally less than average across the state. This was after a couple months of near to above average rainfall in many locations. This is a dry time of year in most areas with the main exception being the Kona section of the Island of Hawaii where this is generally one of the wetter months of the year. The Kona section was one area this month having the greatest negative precipitation anomaly in the state and one of the more significant, in that now is the time they expect heavier rainfall. Overall across the state this is the drier time of ye ar and it does not take much rainfall to make average. Therefore those sections that were below average were often receiving very small amounts of rainfall. In some of the more critical rainfall locations, due to the dependence on catchment water for rainfall, such as the windward sections of Maui and the Island of Hawaii below average rainfall did occur. However, reports from those areas indicate that many sections did receive sufficient rainfall to avoid serious short term water deficits.

During much of July 1998, a ridge of high pressure remained strong across the Pacific to the north northwest of the state. This high pressure position more to the northwest than average, caused much of the island chain in near to above average trade wind conditions and some trade wind shower activity. Some locations due to the consistent direction of the wind and the island's position with respect to cloud areas moving toward the state, received above average rainfall amounts, while many others were below. This added rainfall in select areas has helped relieve some of the very dry conditions there. However, much more rainfall is needed to get beyond the longer term drought situation in some locations. One tropical system, the remains of Hurricane Darby, moved to around 100 miles north of the islands as a disturbance. This did increase the showers in the vicinity, with Kauai receiving the most rainfall.

For a more complete summary, please see the July Precipication Summary from the National Weather Service Honolulu Weather Forecast Office.

American Samoa: We are expecting near record drought conditions for American Samoa. As anticipated in the last Pacific ENSO Update, rainfall for April through August of 1998 was well below normal, but highly variable. At Pago Pago, April rainfall was 0.74 inches (6%), May rainfall was 1.64 inches (17%), June rainfall was 4.72 inches (64%), and July rainfall was only 1.42 inches (23%). In April and May, the South Pacific Convergence Zone (SPCZ) was north and east of Samoa, giving the Samoa region extended periods of dry weather. June, July and August rainfall for the Samoa region has been exclusively from showers embedded in enhanced trade wind flow or from the occasional passage of weak cold fronts. Wet weather is expected to return in October as the South Pacific Convergence Zone redevelops near or over the Samoa region. Tropical cyclone activity in the southern hemisphere will move west of the international date line, reducing the threat to the Samoa Islands area. Rainfall predictions for American Samoa and the region are:

Inclusive Period       % of long-term average

                             Samoa Region
Sep-Oct 1998                     65%
Nov 1998-Jan 1999               110%
Feb-Jun 1999                     90%
July-Sep 1999                    80%

- sources: UOG-WERI and PEAC

Guam/CNMI: After a near record drought for Guam and the CNMI, we expect rains to return to near normal values by Fall. April rainfall for Guam International Airport (GIA) was 1.37 inches (35% of normal values) and that for Andersen Air Force Base (AAFB) was 1.54 inches (32%) for the month. May rainfall at GIA was 1.05 inches (17%), while that at AAFB was 1.07 inches (16%). In Saipan, April and May rainfall temporarily increased from the very dry first three months of the year. Values for April and May at the Saipan International Airport (SIA) were 2.10 inches (60%) and 2.60 inches (47%), respectively. At Capitol Hill, the amounts were 2.10 inches (60%) and 4.20 inches (76%). The April and May rains in the Mariana Islands came mostly from showers embedded in the trade winds. Rainfall increased in June on Guam and in July in the CNMI as the result of heavier rain events associated with upper level disturbances in the Tropical Upper Tropospheric Trough (TUTT). For June, July and August, rainfall at the GIA was 4.52 inches (75%), 5.30 inches (82%) and 4.44 inches (32%), and that at AAFB was 2.65 inches (42%), 4.26 inches (39%) and 5.26 inches (39%). June, July and August rainfall at SIA was 0.91 inch (16% of normal), 5.9 inches (66% of normal), and 5.46 inches (44%). At Capitol Hill, amounts were 0.80 inches (14%), 8.50 inches (94%) and 8.72 inches (70%). Tinian rainfall was 0.95 inches (16%) in June, and 3.90 inches (31%) for July. May values averaged 0.73 inches (13%), while June values were 1.21 inches (19%). Amounts in July increased to 4.40 inches (30%), and August values aren't available. The Sabana region of Rota was more than likely wetter than the northern Golf Resort area.

Rainfall for the Mariana Islands is expected to be below average, as normal monsoon activity will begin late and will be weaker than normal. Most summertime rain will come from disturbances associated with the TUTT and from afternoon showers and thunderstorms. By Fall, tropical cyclone activity and rainfall will return to near normal values. The Mariana Islands will see an increased threat of tropical storms and typhoons from September through early December. Our rainfall predicitions through September 1999 for Guam, Rota, and CNMI are:

Inclusive Period          % of long-term average

                         Guam/Rota          CNMI
Sep-Oct 1999                80%             80%
Nov 1998-Feb 1999           95%             95%
Mar-Jun 1999                85%             85%
July-Sep 1999              100%            100%

- sources: UOG-WERI

Federated States of Micronesia (FSM) :We anticipate a somewhat drier than normal dry season for eastern regions of the FSM, and significantly drier than normal conditions through the Spring of 1999 for near equatorial regions. Near normal rainfall returned to Pohnpei and Kosrae States in May and to Chuuk and Yap States in June. In fact, the rainfall returned more quickly and in greater portions than anticipated. This was primarily the result of disturbances produced on the periphery of upper level low pressure systems embedded in a very active Tropical Upper Tropospheric Trough (TUTT). Rainfall in the eastern FSM decreased somewhat in July, largely as a result of enhanced equatorial easterly winds, brought on by the cooling of equatorial Central Pacific sea surface temperatures. This also brought drier conditions to Nauru and the more equatorial atolls of Pohnpei State huuk States.

Yap State: Rainfall returned toYap in a big way in June, which saw 16.97 inches or 134% of normal rainfall. Rain amounts were 0.21 inches (4%) in April and 2.41 inches (27%) in May. July values fell to 11.99 inches (82% of normal and remained steady in August with 12.03 inches (79%). Nearby, rainfall on Ulithi Atoll for April and May amounted to only 0.44 inches (8%) and 2.66 inches (29%), respectively. Ulithi rainfall in June and July increased, and was 7.87 inches (62%) and 9.73 inches (67%), while August rainfall decreased to 4.19 inches (28%. At Woleai Atoll, rainfall in April was 1.41 inches (11%) and in May was 4.41 inches (36%). June rainfall increased dramatically to (11.86 inches (101%) , but in July and August, amounts decreased to 5.90 inches (49% of normal) and 7.27 inches (48%). While tropical cyclone activity was much reduced in the first half of 1998, we expect the activity to return to normal by late Summer. Thus, northern Yap islands could be subjected to tropical storms and typhoons from September through November, and southern Yap islands could be threatened by tropical cyclones from October through mid-December. Summer rainfall if predicted to be below normal until the summer of 1999, when southwesterly monsoon activity and tropical cyclone activily return to normal.Rainfall observations and predictions forYap and the outer atolls are:

Inclusive Period         % of long-term average

                         Yap              Outer Atolls:
                       Island        S.of 8·N     N. of 8·N

Jun-Aug 1998             96%            66%          52%
Sept 98 - Jun 99         90%            85%          85%
July-Sep 1999           100%           100%         100&

- sources: UOG-WERI

Chuuk State: In April, Weno Island received only 1.13 inches or 9% of normal rainfall. Rains began to return to Chuuk Lagoon in May, when Weno Island recorded 9.96 inches or 81% of normal. During April and May, rainfall at Lukunoch and Polowat averaged 49% and 26% of normal, respectively, but May was much wetter than April at both locations. In June, Weno Island received 10.07 inches (86%), July received 5.43 inches (45%) , and in August 12.89 inches (88%). Rainfall at Lukunoch was16.43 inches (140%) in June and 7.70 inches (64%) July, respectively. July rainfall in Polowat was 4.69 inches (39%). Most rainfall was the result of disturbances associated with the Tropical Upper Tropospheric Trough (TUTT). In July, the TUTT moved northward, decreasing its influence. The Hall Islands and Namanuito Atoll were drier than the more southern islands. While tropical cyclone activity was much reduced in the first half of 1998, we expect the activity to return to normal by Fall. Northern Chuuk could be subjected to tropical storms and typhoons from September through November, and southern Chuuk islands could be threatened by tropical cyclones from October through mid-December. Predicted rainfal for Chuuk State are as follows:

Inclusive Period               % of long-term average

                       Chuuk         Outer Atolls
                       Lagoon    Southern    Northern
Aug-Sep 1998             75%        75%         70%
Oct-Dec 1998             90%        90%         85%
Jan-May 1999             85%        85%         85%
Jun-Sep 1999            100%       100%        100%

- sources: UOG-WERI

Pohnpei State: After several monthsof extremely dry weather, Kolonia received 4.96 inches or 30% of its normal rainfall in April and 16.02 inches or 84% in May. For the same two months, Pingalap measured 3.21 inches (20% of normal) and 11.94 inches (66%), and Nukuoro had 7.14 inches (43% of normal) and 10.18 (56%). June, July, and August rainfall for Pohnpei were 16.19 inches (94% of normal), 8.09 inches (44%), and 14.93 inches (90%). June and July rainfall amounts for Pingalap were 9.97 inches (54% of normal) and 11.50 inches (63%). Nukuoro received 7.78 inches (47%) in June and 5.35 inches (36%) in July, being influenced by the equatorial easterly winds. Most rainfall came from upper level disturbances initiated by the Tropical Upper Upper Tropospheric Trough. We expect somewhat drier than normal conditions in Pohnpei State due to the development of La Niña conditions, which enhances equatorial easterly winds and bring somewhat drier weather. More equatorial islands such as Kapingamarangi and Nukuoro will have drier conditions. Nauru will especially be dry until March 1999, and possibly until June 1999, depending on the strength of the La Niña. Pohnpei State islands will have a reduced threat from tropical cyclones and strong westerly winds over what occurred in 1997. April-July observations predictions for Pohnpei State are as follows:

Inclusive Period          % of long-term average

                     Pohnpei      Outer Atolls:
                     Island    Eastern    Southern 
Apr-May 1998           30%       10%         15%
Jun-Aug 1998           83%       60%         45%
Sep 1998-May 1999      95%       85%         70%
Jun-Sep 1999          100%      100%         95%

- sources: UOG-WERI

Kosrae State: Kosrae was the first locale in Micronesia to emerge from the record-setting, El Niño--produced drought of 1997/98. Significant rains returned to Kosrae in late April, about a month earlier than expected. In April, the Kosrae Airport reported 8.02 inches (37%) and Utwa reported 8.20 inches (38%). In May, amounts rose dramatically to 17.54 inches (93%) at the airport, 17.01 inches (91%) at Utwa, and 13.43 and 13.45 inches (71%) at Tafunsak and Tofol. At all locations in Kosrae, rainfall in June was the heaviest of the year as amounts ranged between 17.58 inches (93%) at Tafunsak and 20.39 inches (107%) at Utwa. Most of the rainfall during these months came from disturbances that moved northward from the southern hemisphere equatorial areas. The mountains of Kosrae also played an important role in producing rain-bearing clouds. As easterly winds strengthened along the equator, rainfall in Kosrae dropped off in July to 12.20 inches (72%) at the airport and to 10.11 inches (59%) in Utwa. In August, the airport reported 13.56 inches (82%). Kosrae State will have a reduced threat from tropical cyclones and strong westerly winds over what was experienced in 1997. Observations and predictions for Kosrae are:

Inclusive Period    % of long-term average

                           Kosrae Island
Jun-Aug 1998                   80-85%
Sep 1998 - Feb 1999            85-90%
Mar-Jun 1999                    80%
July-Sep 1999                  100%

- sources: UOG-WERI

Palau: Rains returned to Palau in May, a few weeks earlier than anticipated. In Koror, the dry period lasted through April, leading to extensive water rationing. In April, only 2.12 inches (24% of normal) fell in Koror and only 2.91 inches (34%) fell in Peleliu. May and June saw large increases in rainfall, with 9.16 inches (81%) and 17.62 inches (102%) on Koror during the respective two months. At Peleliu, 8.64 inches (72% of normal) and 19.51 inches (113%) of rain fell in May and June. In July, values fell to 7.07 inches (39%) in Koror and to 7.26 inches (40%) in Peleliu. Rainfall rebounded somewhat in August with 10.16 inches (68%) at Koror. Most of the rainfall came from upper level disturbances associated with the Tropical Upper Tropospheric Trough (TUTT). By July, these TUTT-induced disturbances had moved north of the island group, probably giving slightly more rain to Kayangel Island. Reduced monsoon activity will keep rainfall below normal for the remainder of the summer. While tropical cyclone activity was much reduced in the first half of 1998, we expect the activity to return to normal by Fall. Thus, northern Palau islands could be subjected to tropical storms and typhoons from late October through mid-December. The observed and expected rainfall for the next 12 months for Palau are as follows:

Inclusive Period              % of long-term average

                    Koror and           Outer Atolls
                    Babelthaup     S. of 8ºN    N. of 8ºN
Apr 1998               24%          30-35%       20-25%
May-Aug 1998           72%          75-80%        ~70%
Sep 1998 - Jun 1999    85%            80%          85%
Jul-Sep 1999          100%           100%         100%


- sources: UOG-WERI

Marshall Islands: Rains returned to the Southern Islands in late May and to the Northern Islands in early July. Rainfall in the southern (northern) Marshall Islands for the first 4 (5) months of 1998 was extremely sparse. At Majuro (representative of southern atolls), rainfall for April was 0.64 (6%) and for May was 6.59 (59%). At Kwajalein (representative of northern atolls including Ebeye), rainfall for April was 0.72 (10%) and for May was 0.87 (9%). In June and July, rainfall amounts at Majuro were 10.51 (91%) and 16.29 inches (125% of normal). August rainfall at Majuro fell to 12.05 inches (105%). At Kwajalein and Ebeye, rainfall was 3.86 (41%) for June, 12.63 (121%) for July, and 11.18 inches (111%) for August. While drinking water is no longer a problem in the Marshall Islands, food items will have to be delivered to outer atolls until the drought-stricken crops and trees recover. Most rainfall has been the result of disturbances associated with upper level cyclones in the Tropical Upper Tropospheric Trough (TUTT). La Niña conditions are expected to materialize by Fall, and should create drier than normal conditions during the Spring of 1999. Tropical cyclone activity for the Marshall Islands will be much less than that in 1997. The greatest threats will be to Wake Island in September and Enewetok and Ujelang Atolls in September and October. Late-season tropical cyclones in the Marshall Islands are not likely. Observed June-August rainfall and predicted rainfall amounts for the Marshall Islands are:

Inclusive Period % of long-term average
                              RMI Atolls
                        Southern     Northern
Jun-Aug 1998              107%        80-91%
Sep 1998 - Feb 1999        90%         85%
Mar-Jun 1999               75%         65%
Jul-Sep 1999              100%        100%

- sources: UOG-WERI


Long-Lead Outlook for Hawaiian Islands issue dated 14 May 1998, from NOAA's Climate Prediction Center (CPC).

ENSO ADVISORY of August 11,1998

SPECIAL SECTION - Experimental Forecasts for Pacific Island Rainfall


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
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
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.

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
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.

HIG #331, 2525 Correa Road, Honolulu, Hawaii 96822
Contact R. Tanabe 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:

Mark Morrissey
Guest Editor, Pacific ENSO Update,
c/o Environmental Verification and Analysis Center (EVAC)
710 Asp Ave., Suite 8
Norman, OK 73069

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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