Pacific ENSO Update
3rd Quarter 2003-Vol. 9 No. 3
CURRENT CONDITIONS
Recent patterns of the atmospheric circulation and
the oceanic sea surface temperature (SST) distribution in Micronesia and in
the central Pacific indicate that the climate of the region has entered a
phase that is neither El Niño nor La Niña: a condition recognized
as El Niño Neutral. The widespread dryness that was expected
to occur in Micronesia through the first six months of 2003 did not materialize,
and most islands received adequate rainfall (Figure
1a,b). Throughout all of Micronesia, rainfall during the first half
of 2003 has been much greater than in most such periods during years that
follow El Niño. Rainfall during July and August has generally
been near normal to slightly below normal in most locations.
Areas of deep convection, including several tropical
disturbances that later moved west and became tropical cyclones northwest
of Yap and Palau, persisted across Micronesia from Palau east to the Republic
of the Marshall Islands (RMI). Most areas experienced episodes of
heavy rain showers and some thunderstorms throughout the first half of 2003.
This type of weather pattern has persisted into July and August: light winds
with scattered showers and thunderstorms, with some intervening periods
of sunny, hot, dry weather. Four tropical cyclones, Tropical Storm
Yanyan, Super Typhoon Kujira, Typhoon Chan-Hom, and Typhoon Soudelor affected
parts of Micronesia in January, April, May, and June respectively.
These early season tropical cyclones largely passed over water and spared
the islands major problems. The exception was serious flooding in
Kolonia, Pohnpei, from heavy rains associated with the passage of Typhoon
Kujira (when it was a tropical storm) near the island. During July
and August, tropical cyclone formation shifted farther to the west, and
areas affected by typhoons included the Philippines, Japan, and China.
Micronesia has enjoyed a welcome break from the numerous tropical storms
and typhoons that plagued the region during 2002. The threat of tropical
storms and typhoons, however, remains near normal for the rest of the year
for the area from Chuuk west to Guam, the CNMI, Yap and Palau. The
threat of tropical storms and typhoons should be reduced for the rest of
the year at islands from Pohnpei east into the RMI.
A suite of international computer forecasts of El Niño
are in general consensus that the climate will remain El Niño neutral
(a climate state that is neither El Niño nor its opposite, La Niña)
for the next six to nine months. The following ENSO Forecast Forum
was posted on the U.S. Climate Prediction Center web site on August 27, 2003:
“Oceanic and atmospheric conditions in the tropical
Pacific were consistent with ENSO-neutral conditions during July 2003. Equatorial
SST anomalies greater than +0.5°C persisted in the region west of the
date line, while negative anomalies remained in the far eastern Pacific,
near the South American coast. During July there was very little net change
in the SST anomalies in the Niño regions.
Since late May positive equatorial upper-ocean temperature
departures have spread eastward into the central and eastern Pacific. This
evolving subsurface pattern is associated with an eastward propagating oceanic
Kelvin wave, resulting from a period of weaker-than-average easterlies in
the central equatorial Pacific that occurred during late May and early June.
SST anomalies in the Niño 3.4 and Niño 3 regions increased
during early June through early July, but then decreased during the last
half of July, as the equatorial easterlies strengthened.
Some atmospheric indices, such as the Tahiti-Darwin
SOI, and central Pacific low-level (850-hPa) zonal wind and OLR, have displayed
considerable month-to-month variability and no consistent trend towards
either La Niña or El Niño since May 2003.
A majority of the statistical and coupled model forecasts
indicate near neutral conditions (Niño 3.4 SST anomalies between
-0.5°C and +0.5°C) through early 2004. This is consistent
with current conditions and the lack of any consistent trend in the oceanic
and atmospheric indices.”
SST
El Niño conditions ended in the spring of
2003 as the sea surface temperature (SST) anomalies decreased across the
equatorial Pacific to below the threshold values for El Niño.
The cooling of the SSTs did not progress to the colder-than-normal values
necessary for La Niña, but generally remain slightly above normal
in the central equatorial Pacific, and a bit colder than normal along the
coast of South America. The SST is slightly warmer than normal throughout
most of Micronesia.
Ocean temperatures at thermocline depth (50-100 m) were 1-2°C
above normal in the central equatorial Pacific and 1-2°C below normal
in the far eastern Pacific near the coast of South America. The temperature
of the subsurface ocean water is now substantially cooler since its peak
warmth in December 2002. At that time the subsurface water was generally
at least 2º C warmer than normal to a depth of about 150 meters in the
equatorial Pacific from 180° east to the coast of South America.
Peak warm anomalies of over 5°C warmer than normal at depths of 100-150
meters occurred between 115°W to 95°W. By July 2003, the subsurface
water was still warmer than normal across much of the equatorial Pacific.
An area of anomalies in excess of +2°C was found at 100-150 meter depth
at the equator from the international date line east to 110°W.
Subsurface waters have become over -2°C colder than normal at 50 meter
depth between 100°W and the South American coast. Recent SST and
subsurface water temperature anomalies have shown much month-to-month variability,
but in general have dropped to levels below the El Niño threshold.
Still, these anomalies are not sufficiently cold for La Niña.
SEA LEVEL
During El Niño, the sea level
falls throughout most of Micronesia. During most El Niño events,
the sea level fall is approximately 0.5 meter below the La Niña high
stands of the sea. The sea level typically drops to its lowest magnitude
at the end of the El Niño year, and then quickly rises to above normal
by May or June of the following year. During the years 1999, 2000,
and 2001, the sea level was well above normal in Micronesia. By December
2002, the sea level throughout most of Micronesia fell to its minimum value.
In some places this was over 40 cm lower than its 1999 high point.
The greatest lowering of the sea level (20 cm below normal) was observed
in the region of Palau and Yap. The sea level fell to nearly 10 cm
below normal all the way east to the northern Marshall Islands. By
February 2003, the sea level had recovered to near normal levels throughout
much of Micronesia, and by June 2003, the sea level was once again above
its long-term average (
Figure
2). The sea level throughout Micronesia should remain near normal
to slightly above normal through the first half of 2004.
SOI
The Southern Oscillation Index (SOI) was near -1.0 from
May 2002 to June 2003. During July 2003 the SOI rose to +0.2, the first
time that the SOI has been positive since February 2002. Nearly all
El Niño events are associated with a persistently negative SOI.
After an El Niño the SOI usually rises to near zero or becomes positive.
The SOI remained negative through the first half of 2003. The abrupt
rise to +0.2 in July 2003 should herald an extended period of SOI values
near zero, or slightly positive.
TROPICAL CYCLONE ACTIVITY
During the first six months of 2003, there were seven
tropical cyclones in the western North Pacific that were numbered by the
Joint Typhoon Warning Center (JTWC) in Hawaii. The Japan Meteorology
Agency (JMA) named six of them. Tropical Storm Yanyan (01W) formed
near Pohnpei in mid-January and traveled toward Guam, giving the residents
a scare so soon after the devastation wrought by Typhoon Pongsona in December
2002. During April 2003, a very powerful tropical cyclone, Super Typhoon
Kujira (02W) formed near Pohnpei and tracked to the south of Guam.
The month of May was very active in the western North Pacific basin with
four tropical cyclones numbered by the JTWC, three of which were named by
the JMA. Tropical Depression 03W was a short-lived system that lived
and died over water east of Luzon. Typhoon Chan-hom (04W) formed in
Chuuk State causing gales and heavy rain there. Chan-hom moved nearly
straight north from Chuuk State and passed well to the east of Guam.
The next two tropical cyclones – Tropical Storm Linfa (05W) and Tropical
Storm Nangka (06W) formed in the South China Sea and affected the Philippines.
Tropical Storm Linfa caused substantial damage and loss of life as it passed
in an unusual west-to-east direction across the island of Luzon. Typhoon
Soudelor (07W) moved through the Ryukyu Islands of Japan after forming north
of Palau. During July and August there were seven more tropical cyclones
in the western North Pacific that were numbered by the JTWC and also named
by the JMA: Typhoon Koni (08W) (a large typhoon when in the South China
Sea that formed southwest of Guam and passed north of Palau), Super Typhoon
Imbudo (09W) (an intense tropical cyclone that made its way into the South
China Sea after passing by Yap as a tropical storm and crossing over Luzon),
Typhoon Morakot (10W) (a tropical cyclone that formed east of the Philippines
and then trekked across the Taiwan Straights into southeastern China), Typhoon
Etau (11W) (a major typhoon for the Ryukyu’s and the Japan main islands),
Typhoon Krounah (12W) (a tropical cyclone that passed almost directly over
Guam on August 19 as a tropical depression, and then passed across the Philippines
and became a typhoon in the South China Sea), Tropical Storm Vamco (a relatively
weak tropical cyclone that passed around the east side of Taiwan and then
made a left turn and made landfall in eastern China), and lastly Typhoon
Dujuan (14W) (an intense typhoon that formed north of Guam and Saipan in
late August and later affected Hong Kong in early September). The total
of seven tropical cyclones in the western North Pacific during the first
six months of the year was one more than the average of nearly six during
that time period. This was unusual for a year following El Niño.
Such years typically have a reduced number of tropical cyclones in the first
half of the year. The seven tropical cyclones in the western North
Pacific during July and August, however, were three short of the normal 11
in the basin during these two months.
Since 2000, the Laboratory for Atmospheric Research
(LAR) at City University of Hong Kong (Professor Johnny C.L. Chan, Chair
and Dean) has been issuing real-time predictions of the annual number of
tropical cyclones affecting the western North Pacific and the South China
Sea (http://aposf02.cityu.edu.hk/~mcg/staff/staff.htm).
For predictions for the entire western North Pacific, different predictors
give rather similar forecasts: it is unlikely that 2003 will see above-normal
tropical cyclone activity over the entire western North Pacific. The
final forecasts call for a normal to below normal number of
tropical cyclones (two less than normal), tropical cyclones reaching at least
tropical storm intensity, as well as typhoons (one less than normal).
Another group (http://tropicalstormrisk.com),
led by Dr. Mark Saunders at the Benfield Greig Hazard Research Centre, University
College London has issued a prediction for a slightly more active season
than normal in the western North Pacific with one more typhoon and
one more intense typhoon than average. These two forecasts are actually
in close agreement that the tropical cyclone activity in the western North
Pacific during 2003 will be near normal.
NOAA's Climate Prediction Center in Washington D.C. routinely monitors
the lastest forecast results from several ENSO models.
The prognostic
discussion for long-lead outlooks outlines these results.
LOCAL VARIABILITY SUMMARIES
State of Hawaii: Two heavy rain events occurred during the
month of August embedded within an overall pattern of moderate to fresh trade
winds. The more serious event occurred on 18 August when heavy trade wind
showers caused stream flooding along the east and northeast facing slopes
of Haleakala on Maui. Seven hikers were rescued in Puohokamoa Stream when
stream levels rose several feet. Near the coast at Oheo Gulch, a tourist
was swept out to sea in elevated stream waters and perished in the surf zone.
The remnants of Tropical Storm Hilda passed to the south of the Big Island
at the time of the event and the enhanced showers may have been associated
with the northern fringe of these remnants. The second heavy rain event of
August involved an area of enhanced tropical moisture that moved into the
Big Island on 5 August. Thunderstorms developed over the Kohala section of
the Big Island and produced minor flooding. No incidents of significant damage
or injuries were reported. Tropical Depression 1C passed south
of the island chain on 15 and 16 August. The depression did produce enhanced
trade winds and a resultant increase in trade wind showers over the eastern
slopes of the Big Island. Rain totals were mostly in the range of 1 to 3
inches in the Hamakua, Hilo, and Puna areas. The rainfall of Hurricane
Jimena occurred on 1 September and will be covered in next month's report.
Kevin Kodama-Senior Service Hydrologist, NWSFO Honolulu, Hawaii
For a more complete summary, and the county by county wrap-ups, please
see the August
2003 Precipitation Summary from the National Weather Service Honolulu
Weather Forecast Office.
American Samoa: Rainfall at Pago Pago Airport for April,
May, and June was 9.33 inches (77%), 19.59 inches (197%), and 7.69 inches
(104%), respectively, amounting to 125% of normal for the 3-month period.
Rainfall at American Samoa was below normal for all months from December
2003 to April 2003, then became above normal starting in May 2003.
During the first half of 2003 the 63.54 inches of rain at Pago Pago was 96%
of the average (Figure
1b).
Rainfall in American Samoa is not as closely tied
to ENSO as it is in other regions of the Pacific. Some prolonged very
dry periods at American Samoa have occurred in association with major El
Niño events, and some prolonged very wet periods have occurred in
years prior to major El Niño events. On average there is not
a consistent ENSO signal in the rainfall. There is a tendency for Samoa
to experience prolonged dry periods in the years following intense El Niño
events, such as 1997-98. Although the period December 2002 through
April 2003 was persistently drier than normal, abundant rains returned in
May.
The return of abundant rainfall in May 2003 was accompanied
by an unfortunate disaster: torrential rains on May 19 produced flash floods
in streams, slope failures, and excessive ponding of water. Four deaths
were reported as well as numerous injuries and extensive damage to roads,
homes, and bridges. At the WSO at the Tafuna airport, 9.50 inches of
rain fell in only four hours. Upwards of 17 inches of rain fell in
24 hours from a convective cell along a shear line. On satellite imagery
this cell did not appear to be anything out of the ordinary.
The first half of 2003 was also noted for an excessive
number of high surf events. The weather office issued more high surf
advisories from October 2002 through July 2003 than during any other year-long
period since the office began high surf advisories in 1992. A three-year-old
boy was washed into the sea and never found on April 28 during one of the
most severe episodes of high surf observed on Tutuila. Condolences
from PEAC go out to the people of Samoa and to the families who suffered
these tragedies.
On a brighter note, American Samoa successfully passed
through its period of highest tropical cyclone threat without being negatively
affected by any cyclone.
Predicted rainfall for American Samoa from October
2003 through September 2004 is:
|
Inclusive Period
|
% of Long-Term Average
|
|
Oct 2003 - Nov 2003
|
95%
|
Dec 2003-Apr 2004 (Rainy
Season)
|
90%
|
|
May 2004 - Sep 2004 (Dry Season)
|
90%
|
source: UOG-WERI
Guam/CNMI: An unexpectedly wet 2003 dry season (January through
June) on Guam has given way to a relatively dry beginning to the 2003 rainy
season in July and August. The 6.25 inches of rain at the Guam International
Airport (GIA) was the fourth driest August total in over 50 years of record-keeping.
In early spring — following December’s onslaught of Typhoon Pongsona — Guam
featured dry brown hillsides and stubby and/or leafless wind-blasted trees.
Greater than average dry season rainfall and increased (but below normal)
rainfall of the wet season have led to rapid growth of shrubs and vines,
and a slow recovery of the foliage of tropical hardwoods. Many trees
(especially wind-blasted stands of Australian Pine) have died.
Rainfall at GIA during April, May, and June was 5.88
inches (125%), 2.91 inches (41%), and 6.12 inches (94%), respectively, amounting
to 81% of normal for the 3-month period. The high spatial variation
and high month-to-month variability of rainfall totals across Guam throughout
the first half of 2003 reflected the small-scale convective nature of the
rainfall events. Surface winds were light for much of the period
from May through August 2003 with no occurrences of strong southwesterly
monsoon winds. Thus, the dominant rainfall regime was scattered daily
island thunderstorms. Andersen Air Force Base (AAFB) measured 11.79 inches
(242%), 3.04 inches (46%), and 12.02 inches (190%), or 151% of the average
rainfall for April through June. The rain gage network at the University
of Guam was one of the driest places on the island during the second quarter
of 2003 with 5.53 inches (141%), 4.04 inches (67%), and 9.41 inches (145%)
during April, May, and June, respectively. During the first half of
2003, the rainfall totals of 25.89 inches at the GIA and 39.31 inches at
AAFB were 78% and 120% of normal, respectively.
On August 29, 2003, lightning struck and killed a
young tourist who was swimming in Tumon Bay. This was the first recorded
lightning death on Guam. Thunderstorms were reported on a total of
26 days at the GIA during June, July, and August.
The expected post-El Niño drought failed to
materialize in the CNMI during January through June. Throughout the
dry season in the CNMI, Saipan and Tinian featured lush healthy forests,
and roadside grasses that were tall, thick, and green. (These islands were
not blasted by December’s Typhoon that devastated Guam.) Rainfall at
the Saipan International Airport (SIA) for April, May, and June was 7.20
inches (257%), 3.30 inches (75%), and 6.23 inches (134%), or 141% of the
average for the period. As on Guam during the first half of 2003, there
was wide variation in the rainfall from place to place. Capitol Hill’s
measured rainfall was much higher overall than the amount recorded at the
airport with 14.6 inches (417%) in April, 7.84 inches (143%) in May, and
6.21 inches (107%) in June. During the first half of 2003, the rainfall
totals of 27.00 inches at the SIA and 49.66 inches at Capitol Hill were 139%
and 204% of normal, respectively.
Rainfall amounts for April, May, and June at the Tinian
Airport were 7.54 inches (215%), 6.85 inches (125%), and 5.65 inches (97%),
respectively. The 3-month rainfall for Tinian Airport was well above
normal at 135%. At Rota Airport, April, May, and June rain amounts
were 10.20 inches (225%), 3.53 inches (56%), and 5.82 inches (94%), respectively.
This gave a 3-month average of 115%. Parts of the western half of Rota
still show effects of the wind blasting from Typhoon Pongsona in December
2002. The rainfall totals of 36.25 inches at Tinian and 33.16 inches
at Rota during the first six months of 2003 were 149% and 108% of average,
respectively.
The very dry conditions that follow an El Niño
year tend to start in November and carry 4-7 months into the year following
El Niño. With an El Niño event in 2002, it was expected
that Guam and the CNMI would have a substantial reduction of rainfall from
November 2002 through June 2003. This did not occur. Several
tropical disturbances, some tropical cyclones, and shear lines provided adequate
rainfall during this period. Later, during July and August, surface
winds were predominantly from the east with no episodes of strong monsoonal
southwesterly winds. This has been associated with much drier conditions
in July and August of 2003 than during July and August 2002 when monsoonal
winds were persistent and several tropical cyclones affected the islands.
Unless there are episodes of strong monsoonal southwesterly winds and accompanying
heavy rainfall, or passages near the island of tropical cyclones, it is likely
that the rainfall for the rest of 2003 will fall somewhat below normal.
The threat of typhoons for Guam and the CNMI should be normal for the remainder
of 2003. This means that approximately two or three tropical cyclones
should brush past Guam and Saipan within 200 miles, but that a direct hit
by an intense typhoon is unlikely.
Predicted rainfall for the Mariana Islands from October
2003 through September 2004 is as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
---
|
Guam/Rota
Saipan/Tinian |
|
Oct 2003 - Dec 2003
|
90%
85% |
|
Jan 2004 - May 2004 (Dry Season)
|
90%
90% |
|
Jun 2004- Sep 2004
|
100%
95% |
source: UOG-WERI
Yap State: Stations on the main island of Yap and on the
atolls of Yap State all began to experienced persistent dryness from November
2002 through February 2003, then many stations were quite a bit wetter than
normal during the second quarter months of April, May and June. The
Weather Service Office near the Yap Airport recorded 6.54 inches (114%) in
April, 22.14 inches (244%) in May, and 11.70 inches (92%) in June, or 147%
of normal rainfall for the three months. Rainfall amounts on Ulithi
were 5.94 inches (121%) in April, 9.64 inches (125%) in May, and 8.56 inches
(79%) in June, or 103% for the 3-month period. Farther south at Woleai
Atoll (which is normally wetter than Yap and Ulithi year-round), persistent
dryness has occurred throughout most of October 2002 through May 2003.
The rainfall there was 5.75 inches (52%) in April, 15.99 inches (131%) in
May, and 7.7 inches (59%) in June, for a 3-month average of 81%. Heavy
rainfall in Yap State during May 2003 was associated with some intense mesoscale
convective systems that accompanied weak tropical disturbances. During
the first six months of 2003, the rainfall totals of 55.68 inches at the
Yap airport, 34.02 inches at Ulithi, and 39.29 inches at Woleai were 119%,
86% and 39% of normal, respectively.
The tropical cyclone threat at Yap should perhaps
be slightly higher than normal through the rest of 2003. The focus
of tropical cyclone activity in the western North Pacific seems to have shifted
west from where it was in 2002 when Guam, Chuuk, and Pohnpei took the brunt
of several tropical cyclones.
Predicted rainfall for Yap State from October 2003
through September 2004 is as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
Oct 2003 - Dec 2003
|
95%
|
|
Jan 2004 - Jun 2004 (Dry Season)
|
95%
|
|
Jul 2004 - Sep 2004
|
100%
|
source: UOG-WERI
Chuuk State: Rainfall at islands and atolls throughout most
of Chuuk State has been abundant for most of the first half of 2003.
Only some of the atolls in the north experienced a prolonged modest reduction
of rainfall that began in October 2002 and persisted through March 2003.
During April, May, and June, the Weather Service Office at Weno Island measured
12.47 inches (101%), 13.93 inches (114%), and 13.3 inches (113%). This
amounted to 109% of normal rainfall for the 3-month period. At Lukunoch,
rainfall for April, May, and June was 7.59 inches (61%), 19.92 inches (163%),
and 11.55 inches (99%) for the respective months. This amounted to
108% of normal for the 3-month period. At Polowat in the western atolls,
the rainfall for April, May, and June was 8.11 inches (135%), 23.99 inches
(267%), and 11.66 inches (93%), or 159% of normal for the 3-month period.
For the first six months of 2003, the rainfall totals of 62.43 inches at
Weno, 58.51 inches at Lukunoch, and 60.13 inches at Polowat were 102%, 95%,
and 125% of normal respectively.
Three tropical cyclones affected Chuuk State in the
first half of 2003: the tropical disturbance that became Tropical Storm
Yanyan in January, Typhoon Kujira in April, and Typhoon Chan-Hom in May.
Yanyan was only a tropical disturbance when it passed through Chuuk State
and provided some beneficial rains. Typhoon Kujira passed to the north
and did not have any major impacts. Typhoon Chan-Hom formed near Chuuk
State and passed very close to the west of Weno on May 20 as a tropical storm
and produced very heavy rainfall in some locations and gusty southerly winds.
Typhoon Krouna formed just north of the main islands of Chuuk in mid-August,
but had no serious effects. The threat from tropical cyclones for Chuuk
State for the rest of 2003 should be near normal.
Predictions for Chuuk State from October 2003 through
September 2004 are as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
Oct 2003 - Dec 2003
|
95%
|
|
Jan 2004 - Jun 2004
|
100%
|
|
Jul 2004 - Sep 2004
|
95%
|
source: UOG-WERI
Pohnpei State: Rainfall at Pohnpei State has been heavier
and more frequent than expected. Anticipated moderate drought conditions
did not materialize with this current ENSO event. With the notable
exception of Kapingamarangi, the islands and atolls of Pohnpei State experienced
slightly drier than normal conditions during most of the months from October
2002 through March 2003. At the Weather Service Office at Kolonia,
the April, May, and June rainfall totals were 31.84 inches (194%), 29.97
inches (157%), and 12.66 inches (74%), respectively. This amounted
to a 3-month total of 74.47 inches or 141% of average precipitation.
At Pingelap, observed rainfall in April, May, and June was 8.21 inches (48%),
18.61 inches (109%), and 6.34 inches (39%), respectively, for a 3-month amount
of 66%. At Nukuoro, April through June precipitation amounts were 11.29
inches (75%), 15.13 inches (103%), and 6.97 inches (57%), respectively, for
a 3-month amount of 80%. Rainfall at Kapingamarangi was approximately
14 inches during each month from January through March, but decreased slightly
in the second quarter with totals during April through June of 7.28 inches
(54%), 11.93 inches (115%), and 10.91 inches (150%) respectively, for a 3-month
amount of 97%. The 109.33 inches of rain at the WSO Kolonia, for the
first six months of 2003, was the highest recorded rainfall in Micronesia
and was 121% of the average for those months. Six-month rainfall totals
were 66.42 inches (74%) at Pingelap, 62.82 inches (81%) at Nukuoro, and 74.36
inches (107%) at Kapingamarangi.
Tropical cyclones and several tropical disturbances
that later became named tropical cyclones affected Pohnpei State through
most of 2002 and again during the first half of 2003. Since Kujira’s
passage near Pohnpei in April, however, most of the tropical cyclone activity
in the western North Pacific has shifted west and has not affected the eastern
Carolines or the Marshall Islands. Despite an early start to tropical
cyclone activity in Pohnpei, the threat of tropical cyclones should be normal
for the rest of 2003.
In cooperation with the Conservation Society of Pohnpei,
and with help from the Nature Conservancy and the local office of the National
Weather Service, researchers from the University of Guam (UOG) have set up
a network of electronic and manual rain gages all over Pohnpei from coastal
locations to the highest mountain peak in the center of the island.
These rain gages (supported by a grant to the UOG from the United States
Geological Survey) are intended to supply information about the distribution
of rainfall on the island to help water resource managers and other groups
to effectively care for Pohnpei’s unique rain forest, water resources, and
agriculture. The network was activated on June 6, 2003, and the first
data set was collected 50 days later on August 15, 2003. During those
first 50 days, 22 inches of rain fell at the airport and at the Mayor’s Office
near Nan Madol. Twenty-six inches of rain occurred inland and upslope
from the Mayor’s Office on a ridge clearing in Nihpit. On the top of
the highest mountain, Nahna Laud, 41 inches of rain fell during that
50-day period. Other rain gages are at the College of Micronesia, and
at cooperative observing sites managed by the National Weather Service (Figure
3).
Predicted rainfall for Pohnpei State from October 2003
through September 2004 is as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
---
|
Pohnpei Islands and Atolls
Kapingamarangi |
|
Oct 2003 - Dec 2003
|
95%
90% |
|
Jan 2004 - Jun 2004
|
100%
90% |
|
Jul 2004 - Sep 2004
|
95%
85% |
source: UOG-WERI
Kosrae State: Kosrae experienced one of the largest rainfall
deficits (with respect to normal) in Micronesia during the first half of
2003. Rainfall at Kosrae (SAWRS) during April, May, and June was 15.5
inches (72%), 20.79 (111%), and 8.64 inches (45%) respectively. The
3-month second quarter total of 44.93 inches was 76% of the normal total
of 59.46 inches. For the first half of 2003, the 71.32 inches of rain
at Kosrae (SAWRS) was 71% of average. The three other Kosrae stations
(Tofol, Tafunsak, and Utwa) had April, May and June totals of 50.95 inches
(86%), 34.45 inches (58%), and 45.36 inches (76%), respectively. During
the first half of 2003, Tofol, Tafunsak, and Utwa had 88.64 inches (89%),
67.82 inches (62%), and 78.98 inches (80%), respectively. The modest
rainfall deficit on Kosrae during the first half of 2003 has had no significant
impact on water resources or vegetation.
Rainfall for Kosrae State is expected to be near normal
for the remainder of 2003. The threat of tropical cyclones to Kosrae
will be slightly below normal for the rest of 2003.
Predicted rainfall for Kosrae State from October 2003
through September 2004 is as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
Oct 2003 - Dec 2003
|
90%
|
|
Jan 2004 - Jun 2004
|
95%
|
|
Jul 2004 - Sep 2004
|
90%
|
source: UOG-WERI
Republic of Palau: In Palau, dry conditions associated with
El Niño tend to set it in as early as September of the El Niño
year and carry into the summer of the following year. In keeping with
El Niño in 2002, the first half of 2002 was generally drier than normal.
Dry conditions did not persist into 2003. Conditions at Palau
were wetter than anticipated during the first two quarters of 2003.
Rainfall at the Weather Service Office at Koror during April, May, and June
was 8.82 inches (102%), 17.15 inches (143%), and 13.90 inches (80%), respectively.
The 3-month average was 105% of normal. For the 3-months of April,
May, and June, the monthly rainfall distribution at Nekken Forestry was slightly
wetter overall than at the Weather Service Office in Koror with 5.92 inches
(68%), 17.68 inches (147%), and 19.72 inches (114%). Farther south
at Peleliu, it was drier, and rainfall totals for April, May, and June were
7.62 inches (85%), 18.54 inches (155%), and 12.13 inches (71%) respectively.
For the first six months of 2003, the rainfall totals were 69.88 inches (106%)
at Koror, 75.07 inches (114%) at Nekken Forestry, and 62.76 inches (95%)
at Peliliu.
Two tropical cyclones formed in Micronesia in the
first three months of 2003, and passed well to the northeast of Palau:
Tropical Storm Yanyan in January and Super Typhoon Kujira in April.
Neither of these tropical cyclones had any major effect in Palau. During
June, July and August, Palau was affected by the beginning stages of typhoons
Soudelor, Koni, Imbudo, and Etau. The dominant effect of these
tropical cyclones was periods of heavy rain showers. The threat from
tropical cyclones will be slightly higher than normal in Palau for the remainder
of 2003 as the focus of typhoon activity has shifted west from where it was
in 2002. Rainfall for Palau is expected to be near normal for the remainder
of 2003.
Predicted rainfall for Palau from October 2003 through
September 2004 is as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
Oct 2003 - Dec 2003
|
100%
|
|
Jan 2004 - May 2004
|
90%
|
|
Jun 2004 - Sep 2004
|
95%
|
source: UOG-WERI
Republic of the Marshall Islands (RMI): After abundant rainfall
during most of 2002 in the central and southern RMI, the first quarter of
2003 saw near normal rainfall. Only in northern atolls, such as Kwajalein,
Wotje, and Utirik did dry conditions set in late in 2002, and continue into
the first quarter of 2003. During the second quarter of 2003, however,
near normal rainfall occurred throughout the RMI. The Majuro weather
station measured 13.35 inches (130%), 10.55 inches (94%), and 11.5 inches
(99%) during April, May, and June. For the 3-month period, the average
for Majuro was 107% of normal. Rainfall at Kwajalein (and nearby Ebeye)
was 12.14 inches (161%) in April, 10.57 inches (106%) in May, and 6.59 inches
(69%) in June, for a three-month average of 108%. Other atolls in the
northern part of the RMI such as Wotje and Jaluit reported drier totals of
about 60% of normal for the second quarter of 2003. For the first six
months of 2003, the rainfall totals were 55.44 inches (99%) at the Majuro
weather station and 36.49 inches (93%) at Kwajalein.
After weak or moderate El Niño events (such
as 2002), the rainfall at Majuro, Kwajalein and the northern islands of the
RMI tends to be below normal, but at atolls south of 6°N it remains near
normal. The northern atolls of the RMI were one of the few regions
in Micronesia where some extended periods of dry weather occurred during
the first half of 2003.
During 2002, tropical cyclone activity shifted east
of normal in the western North Pacific basin, and westerly winds pushed as
far east as the central and southern Marshall Islands. Many tropical
disturbances moved through the RMI, some of which later moved west and became
named tropical cyclones. During the first half of 2003 the monsoon
trough retreated west closer to its normal location, and easterly winds prevailed
in the Marshall Islands. No numbered or named tropical cyclones affected
the RMI during the first half of 2003, and for the remainder of 2003 the
tropical cyclone threat should be slightly reduced.
Predicted rainfall for the RMI from October 2003 through
September 2004 is as follows:
|
Inclusive Period
|
% of Long-Term Average
|
|
---
|
S. of 6°N
6°N to 8°N N. of
8°N |
|
Oct 2003 - Dec 2003
|
90%
100%
90% |
|
Jan 2004 - May 2004
|
90%
90%
85% |
|
Jun 2004- Sep 2004
|
90%
95%
90% |
source: UOG-WERI
APPENDICES:
Long-Lead
Outlook for Hawaiian Islands issue dated 18 September 2003, from NOAA's
Climate Prediction Center (CPC).
ENSO ADVISORY: issued by Climate Prediction Center/NCEP on
September 11, 2003
Current atmospheric and oceanic conditions in the
tropical Pacific are near average and do not support the development of either
La Niña or El Niño in the next few months. Equatorial sea-surface
temperature anomalies greater than +0.5°C persisted in the region west
of the date line, while near-zero anomalies dominated the equatorial Pacific
east of 150°W. During August very little net change was observed in the
SST anomalies in the Niño regions.
Beginning in late May positive equatorial upper-ocean
temperature departures spread eastward into the central and eastern Pacific.
This evolving subsurface pattern was associated with an eastward propagating
oceanic Kelvin wave, resulting from a period of weaker-than-average easterlies
in the central equatorial Pacific that occurred during late May and early
June. SST anomalies in the Niño 3.4 and Niño 3 region increased
during early June through early July, but then decreased during the last
half of July and remained fairly steady during August.
Some atmospheric indices, such as the Tahiti-Darwin
SOI, and central equatorial Pacific low-level (850-hPa) zonal wind and OLR,
have displayed considerable month-to-month variability since May 2003 and
no consistent trend towards either La Niña or El Niño.
A majority of the statistical and coupled model forecasts
indicate near neutral conditions (Niño 3.4 SST anomalies between -0.5°C
and +0.5°C) for the remainder of 2003 and early 2004. This is consistent
with current conditions and the lack of any consistent trends in the suite
of oceanic and atmospheric indices.
SPECIAL SECTION-Markov Model for Pacific SST and sea level
These are the latest results of a CPC model being produced
by Dr. Yan Xue. Forecasts of the tropical Pacific SST and sea level
anomalies are presented here using a linear statistical model (Markov model).
The Markov model is constructed in a reduced multivariate EOF space of observed
SST and sea level analysis using the methodology of Xue et al 2000.
The model is trained for the 1981-1998 period.
The SST is the NCEP SST analysis and the sea level is
from the NCEP ocean analysis. All the data are monthly values averaged
in grid boxes of 6 degrees in longitude and 2 degrees in latitude, and cover
the tropical Pacific region within 19 degrees of the equator.
Forecast
SST Anomaly (Degree, 3-Mon. Average)
Forecast
Sea Level Anomaly (cm, 3-Mon. Average)
The full suite of Dr. Xue's model results are updated monthly and is available
at:
<http://www.cpc.ncep.noaa.gov/pacdir>
SPECIAL SECTION-Experimental Forecasts for Pacific Island Rainfall
The latest results from the CPC statistical model
for all predicted locations are shown below. This map-like presentation
applies only to two particular seasons (September - November 2003 and December
2003 - February 2003) of the 13 three month periods out to a year in advance
that are available from the model. The full time series in graphs
and tables are updated monthly on the internet at:
<http://www.cpc.ncep.noaa.gov/pacdir/CCA11.html>.
Negative numbers are forecasts for less
than normal rainfall while positive numbers are forecasts for greater than
normal rainfall. The size of the number (not the value
of the number) indicates how accurate the forecast is expected to be, on
the average, for the station at the given time of year and the forecast lead
time. There are three sizes: the smallest size indicates low skill,
the medium size indicates moderate skill, and the largest size indicates
a relatively high skill. The value of the numbers tell how large a deviation
from normal is expected. These values are in standardized units that
indicate how typical (or atypical) the rainfall conditions are expected to
be relative to the station’s normal climatology. For example, numbers
from 0 to 25 (or 0 to -25) are small deviations, indicating conditions
that would be considered typical of the climate for the station and the time
of year. Deviations from 25 to 60 (or -25 to -60) are moderate deviations,
indicating somewhat wetter (or drier) conditions than would be expected for
the station and the time of year. Deviations of over 60 (or less than
-60) are large deviations, indicating much wetter (or drier) conditions than
normal for that location and time of year.
Sites Covered:
(list not complete, selected sites only)
1. Hawaii: Hilo, Kahului, Honolulu, Lihue
2. Guam: Anderson AFB, Guam WSFO
3. Johnston Island
4. Koror WSO, Palau
5. Kwajalein Atoll
6. Majuro WSO, Marshall Is.
7. FSM: Pohnpei WSO, Yap WSO, Chuuk WSO
8. Wake Island
9. Henderson, Solomon Islands
10. Luganville, Vanuatu
11. New Caledonia: Koumac, Noumea
12. Funafuti, Tuvalu
13. Fiji: Rotuma, Undu Point, Nadi
14. Hihifo, Wallis & Futuna
15. Tonga: Niuatoputapu, Vavau
16. Rarotonga, Cook Islands
17. French Polynesia: Atnona, Bora Bora, Papeete, Takaroa,
Rikitea, Tubai, Rapa
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 PREDICTIONS 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 at Manoa
HIG #225, 2525 Correa Rd.
Honolulu, HI 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 INSTITUE (WERI):
Lower campus, University of Guam
UOG Station, Mangilao, Guam 96923
Contact M. Lander at 671-735-2685 for information on tropical
cyclones and climate in the Pacific Islands.
NOAA National Weather Service-Pacific Region
WEATHER SERVICE FORECAST OFFICE (WSFO)
3232 Hueneme Road, Barrigada, Guam, 96913
Contact C. Guard at 641-472-0900 for further information on tropical cyclones
and climate in the Pacific Islands.
University of Hawaii at Manoa
School of Ocean and Earth Science and Technology (SOEST)
Department of Meteorology
HIG #350, 2525 Correa Rd.
Honolulu, HI 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:
University of Hawaii at Manoa
School of Ocean and Earth Science and Technology (SOEST)
Department of Meteorology
HIG #350, 2525 Correa Rd.
Honolulu, HI 96822
Contact R. Schneider at 808-956-2324 for more information on ENSO-related
climate data for the Pacific Islands.
Contact C. Anderson at 808-956-3908 for more information on Pacific
ENSO Update and applications.
For further information, please contact:
Rebecca Schneider
Editor, Pacific ENSO Update,
Pacific ENSO Applications Center
c/o Dept. of Meteorology, HIG Room 350
University of Hawaii - Manoa Campus
2525 Correa Road - Honolulu, HI 96822
Tel: 808-956-2324 Fax: 808-956-2877
E-mail: rsschnei@hawaii.edu
Publication of the Pacific ENSO Update is supported in part by
the National Oceanic and Atmospheric Administration (NOAA),
National Weather Service-Pacific Region Headquartersunder contract
no. AB133W-02-SE-056. The views expressed herein are those of the
author(s) and do not necessarily reflect the views of NOAA,
any of its sub-agencies, or cooperating organizations.
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