Area Forecast Discussion
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FXPQ60 PGUM 152053
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Area Forecast Discussion
National Weather Service Tiyan GU
653 AM ChST Sat Dec 16 2017

.Marianas Synopsis...
Satellite shows some deep convection about 100 miles south of Guam,
but the Marianas waters have only mostly cloudy skies with isolated
showers and moderate trade winds. The buoys are reporting combined
seas between 5 and 6 feet. Well south of Guam, JTWC invest area 97W
is producing showers and thunderstorms over a large area between the
equator and 8N from 139E to 150E.

&&

.Discussion...
Refreshed winds out to 5 days from the latest GFS, as winds look to
be a bit stronger the next couple of days than previous forecasts
indicated. Otherwise, little change to the forecast for now, until
the models can get a more consistent idea of how 97W is likely to
develop and move. Both GFS and ECMWF eventually move a cyclone WNW
south of Guam over the next few days, but differ on timing and track.
The 12Z runs of both models keep 97W well south of Guam, but the GFS
varies more from run to run, and gives the Marianas more wind in
general than the ECMWF, along with more rain. But the GFS is still
pretty dry for the Marianas Sunday through Wednesday.

&&

.Marine...
Winds have increased a bit as pressure falls south of 10N, and should
now be moderate to fresh today through Monday, and fresh to strong
thereafter. Small craft conditions appear likely by Tuesday, with
seas exceeding 10 feet and winds rising to 20-25 kt.

&&

.Eastern Micronesia and Chuuk...
A modest convergence zone associated with moderate to fresh trade
winds will keep periodic showers and possibly some thunderstorms
near Majuro and Pohnpei thru Sunday and Kosrae thru Monday. This
same feature will also produce similar conditions for Chuuk by late
tonight. Starting Sunday evening, a much drier fresh to strong trade
surge should usher in pleasant but windy conditions across the region
from east to west. Things near Chuuk might remain unstable next week,
depending on the future movement of a tropical disturbance currently
southwest of the island near 4N147E. If it takes a northwest track,
it could prolong convergent trades over the island. On the other
hand, a west-northwest track would allow drier trades to arrive from
the east.

Moderate trade-wind swell and wind waves should keep marginally
hazardous surf on Kosrae thru Sunday afternoon. By later tonight,
trade-wind swell and wind waves will start to build higher across
the entire region. This will spread hazardous surf into the Marshall
Islands on Monday and possibly to Pohnpei and Chuuk States on
Tuesday. Seas from Chuuk State eastward to the Marshalls will also
approach Small Craft Advisory levels by Sunday and Monday. Finally,
a new King Tide cycle will start on Sunday. Therefore, need to
monitor for possible inundation on Kosrae and Majuro.

&&

.Western Micronesia...
A tropical disturbance, JTWC suspect area 97W southwest of Chuuk near
4N147E is starting to become better organized this morning.
Widespread deep convection can be seen flaring up surrounding the
center. A mid-level vorticity center is also visible just north of
the surface center. A monsoon trough extends northwestward from this
disturbance across Yap to Tropical Storm Kai-Tak near the central
Philippines. Converging winds near the trough axis will keep a few
showers and thunderstorms near Koror and Yap thru this evening. As
97W slowly tracks west-northwestward tonight and Sunday, it will
introduce converging west to northwest winds over Koror and Yap.
Therefore, do anticipate increasing shower coverage for both places
by Sunday morning. Heavy showers and gusty winds are probable from
Sunday night thru Tuesday as 97W passes thru far western Micronesia.
Depending on the future development of 97W, heavy rain and higher
winds are possible but have not yet included in the forecast.

Latest ASCAT satellite imagery reveals that fresh to strong monsoonal
winds south of Tropical Storm Kai-Tak have weakened this morning.
This should allow the southwest swell to subside across Palau and
cause surf to drop below hazardous levels later tonight. Swell and
winds will gradually build across the area over the next few days as
97W approaches from the southeast. There is a good potential for
marine conditions to become hazardous for small craft operation by
Sunday night or Monday. Depending on the future evolution of 97W`s
wind field and swell direction, hazardous surf is also possible.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
Marianas Waters...None.

&&

$$

Middlebrooke/Chan



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