Pacific ENSO Update

3rd Quarter, 2008 Vol. 14 No. 3

FSM Flag Federated States of Micronesia

Yap State: Yap Island and the outer islands of Yap State were among the few locations where rainfall was deficient during the first half of 2008. Six-month rainfall totals at the Yap WSO and at nearly all other Yap State recording locations were 80% or less of their respective normal values. Several tropical disturbances passed through Yap State during the 2nd Quarter of 2008. These systems provided abundant rainfall to locations in the Republic of Palau, but failed to generate any
substantial rain within Yap State. June was drier than May at all locations in Yap State, a reversal of the normal month-by-month increase in rainfall that is expected this time of year. Aside from being somewhat dry, the weather in Yap State was otherwise uneventful during the first half of the year. Woleai continued its long string of very dry weather, and was the driest recording station in terms of percent of normal rainfall see Fig. 1b) in Micronesia for January – June 2008.

Yap State Rainfall Summary 2nd Quarter and 1st Half 2008

Station   April May June 2nd Qtr
1st Half
Yap Island
Yap WSO
 Rainfall (inches)
6.93
9.69
5.23
21.85
37.61
% of Normal
124%
119%
39%
80%
83%
Dugor*
 Rainfall (inches)
5.76
14.47
3.37
23.60
36.36
% of Normal
103%
178%
25%
86%
78%
Gilman*
 Rainfall (inches)
4.94
10.66
5.71
21.31
37.41
% of Normal
89%
131%
42%
77%
80%
Luweech*
 Rainfall (inches)
6.13
7.21
5.00
18.34
33.92
% of Normal
110%
88%
37%
67%
73%
Maap*
 Rainfall (inches)
8.36
11.11
3.69
23.16
38.61
% of Normal
150%
136%
27%
84%
83%
North Fanif*
Rainfall (inches)
6.96
12.13
5.65
24.74
36.83
% of Normal
125%
149%
42%
90%
79%
Rumung*
 Rainfall (inches)
6.33
12.10
7.12
25.55
37.04
% of Normal
113%
148%
53%
93%
79%
Tamil*
 Rainfall (inches)
7.18
10.19
5.45
22.82
35.98
% of Normal
129%
125%
40%
83%
77%
Outer Islands
Ulithi
 Rainfall (inches)
4.41
9.20
6.84
20.45
31.20
% of Normal
90%
119%
63%
87%
78%
Woleai
 Rainfall (inches)
6.52
5.76
4.04
16.32
28.58
% of Normal
59%
47%
31%
45%
46%
* Long term normal is not established for these sites.

Climate Outlook: All of the islands of Yap State should have near normal rainfall for the next three months (the heart of Yap’s rainy season), and adequate rainfall is expected through the end of the year. Rainfall at Woleai may remain somewhat below normal from August through September as the monsoon trough is expected to stay mostly well to its north. (A similar period of relative dryness was seen in Woleai during August – October 2007.)

Stronger than normal easterly winds along the equator and sub-surface ocean heating in the western North Pacific will keep sea levels above normal around Yap. Tropical cyclone activity in the western North Pacific is expected to be higher than it was during the quiet 2007 season. From August to December 2008, two or three typhoons should pass to the north of Yap Island and Ulithi producing gusty westerly winds and hazardous seas in the island waters. The odds of damaging winds from a tropical cyclone on Yap or any of its northern atolls will be approximately 10% for the remainder of 2008, which represents a normal risk.

Predicted rainfall for Yap State from July 2008 through June 2009 is as follows:

Inclusive Period
% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
Yap and Ulithi
Woleai

July – September 2008
(Heart of Next Rainy Season)

95%
(39.13 inches)
85%
(34.26 inches)

October - December 2008
(End of Next Rainy Season)

100% 100%

January - March 2009
(1st Half of Next Dry Season)

100% 90%

January - April 2009
(End of Next Dry Season)

100% 100%
Forecast rainfall quantities represent BEST ESTIMATES given the probabalistic forecast for each particular season and station.

source: UOG-WERI