Pacific ENSO Update

3rd Quarter, 2007 Vol. 13 No. 3

FSM Flag Federated States of Micronesia

Yap State:  Rainfall throughout Yap State during the first half of 2007 was generally abundant,
thanks to a very wet month of May. Six-month totals at all Yap Island locations were in the range of 50 to 55 inches, which is approximately 5 inches above the typical value for the period. Nearly 30% of the Yap Island rainfall during the first half of 2007 occurred in the month of May. A substantial portion of the May 2007 rainfall was associated with Typhoon Yutu, which passed close by to the north of Yap Island in mid-May. Because of the wet May at Yap Island, the 2nd Quarter and first-half-of-2007 rainfall there surpassed the amount experienced at the normally wetter Woleai. In a more typical pattern, Ulithi received less rainfall than the Yap WSO. The total of 56.18 inches at North Fanif on Yap Island was the highest recorded value for all of Yap State during the first six months of 2007.

Yap State Rainfall Summary 2nd Quarter 2007

Station   Apr. May June 2nd Qtr
Predicted (2nd Qtr)
1st Half 2007
Yap WSO Rainfall (inches)
6.99
16.32
10.90
34.21
23.11
52.24
% of Normal
121%
180%
86%
124%
85%
112%
Dugor* Rainfall (inches)
9.16
17.35
9.79
36.30
23.11
55.34
Gilman* Rainfall (inches)
4.96
15.67
11.38
32.01
23.11
50.00
Luweech* Rainfall (inches)
6.84
16.36
10.09
33.29
23.11
52.50
Maap* Rainfall (inches)
8.91
12.97
11.38
33.26
23.11
48.75
North Fanif* Rainfall (inches)
10.47
17.41
10.95
38.83
23.11
56.18
Rumung* Rainfall (inches)
9.77
12.79
9.06
31.62
23.11
51.58
Tamil* Rainfall (inches)
11.51
15.53
11.34
38.38
23.11
49.38
Ulithi Rainfall (inches)
7.47
9.52
8.31
25.30
19.91
39.37
% of Normal
152 %
124%
76%
108%
85%
99%
Woleai Rainfall (inches)
10.41
11.68
7.57
29.84
31.97
51.88
% of Normal
95%
97%
62%
82%
90%
83%
Predicted rainfall refers to forecast made in 1st Quarter 2007 PEAC Newsletter.
* Long term normal is not established for these sites.

Climate Outlook: Easterly trade winds should continue to dominate the flow in eastern Micronesia (Pohnpei and eastward), and keep rainfall average to slightly below average there. Monsoon and storm activity will have more influence in western Micronesia (Chuuk and westward, including all islands of Yap State), where the rainfall should be average to slightly above average. The trade winds and sub-surface heating in the western North Pacific will keep sea levels above normal. Tropical cyclone activity is expected to be below normal throughout the entire western North Pacific basin during 2007. From August through the remainder of the year, however, 2 or 3 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 atolls will be approximately 5 to 10% for the remainder of the year, which represents a normal risk.

Predicted rainfall for Yap State from August 2007 through July 2008 is as follows:

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

Aug – Oct 2007
(Heart of Next Rainy Season)

100%
(40.19 inches)
110%
(44.00 inches)

Nov 2007 – Feb 2008
(Onset of Next Dry Season)

110% 110%

Feb – Apr 2008
(Heart of Next Dry Season)

100% 100%

May – July 2008
(Onset of Next Rainy Season)

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

source: UOG-WERI