Area Forecast Discussion
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FXPQ60 PGUM 150933

Area Forecast Discussion
National Weather Service Tiyan GU
722 PM ChST Fri Dec 15 2017

.Marianas Synopsis...East trade-winds and isolated showers prevail
across the Marianas this afternoon.


Made no changes to the forecast. Low-level moisture and upper-
level cirrus will keep skies mostly cloudy tonight. GFS and UKMET
hint at an increased chance of showers Saturday night. It appears
that it will be coming from an area of showers now to the
southeast of the Marianas. Not certain on rainfall coverage and at
any rate if it did occur it would only cross over Guam. Believe
cloud cover will be mostly cloudy but shower coverage will remain
predominantly isolated. Deep-layer moisture decreases and only
expect partly cloudy skies and isolated showers Sunday through

The question in the forecast still centers around a circulation
southwest of Chuuk this afternoon near 3N150E. Models continue to
show the circulation moving northwest through next week. On next
Thursday night GFS has it north of Yap, ECMWF south of Yap, JMA,
CMC and NAVGEM show it west-northwest of Yap. All models agree
that the circulation will not have any direct effect on the
Marianas no matter how strong it gets. Models show the pressure
gradient between the circulation and high pressure to the north
causing breezy conditions across the Marianas through next week.
Deep- layer moisture will be lacking through at least the first
half of the coming week with isolated showers all that are
expected over the local area. GFS is hinting at the possibility of
scattered showers and isolated thunderstorms the second half of
the coming week. GFS is the model predicting the circulation
moving the farthest north. If the system treks farther south as
the other models indicate then showers would remain isolated. With
this type of uncertainty left shower coverage as isolated.


Ipan, Tanapag and Ritidian buoys show sea heights around 5 to 7 feet.
Satellite altimerty depicts sea height at 5 to 6 feet. All three
buoys show an east swell. Ritidian and Tanapag buoys show a northwest
swell. Model data does show the east swell persisting through the
forecast while the northwest swell remains through at least

Sea height of 5 to 7 feet are expected through Sunday. Seas are
predicted to start to increase Sunday night. As mentioned above, the
winds will increase next week. Sea heights may reach 10 feet by
Tuesday. With sea height and wind speeds elevated a small craft
advisory will likely be needed some time next week.


.Tropical systems...
As previously mentioned the big question in the forecast still
centers around a circulation...Invest area 97W...southwest of
Chuuk this afternoon near 3N150E. Models continue to show the
circulation moving northwest through next week. Next Thursday
night GFS has it north of Yap, ECMWF south of Yap, JMA, CMC and
NAVGEM show it west-northwest of Yap. Models are hinting at the
circulation gradually increasing in strength through the coming
week. There is some degree of uncertainty on the systems track
and predicted intensity. A Special Weather Statement has been
issued for Invest Area 97W. This weather feature will be closely
monitored for any signs of further development.


.Eastern Micronesia...
The focus of trade-wind convergence and showers remains in an area
from northern Pohnpei and Kosrae States to just south of Majuro and
eastward over the Date Line. Most showers have moved southeast of
Majuro this afternoon. Fair weather persists for Pohnpei and Kosrae
today, but there will be isolated thunderstorms near Kosrae through
Saturday and near Pohnpei through this weekend. ASCAT Analysis shows
fresh to strong trade winds just northeast and east of the Marshall
Islands, and these winds will bring breezy weather to Majuro, Kosrae
and Pohnpei over the weekend into next week.

Moderate trade-wind swell and wind waves should keep marginally
hazardous surf on Kosrae thru Saturday afternoon. Starting Saturday
night and Sunday, trade-wind swell and wind waves will build higher
across the entire region. This will spread hazardous surf to the
Marshall Islands and possibly to Pohnpei and Chuuk States. Seas from
Chuuk State eastward to the Marshalls might also reach Small Craft
Advisory levels. Finally, a new King Tide cycle will start this
weekend. Therefore, need to monitor for possible inundation on Kosrae
and Majuro.


.Western Micronesia...
A Special Weather Statement was issued for this area since weather
will be inclement and unstable through the weekend into next week,
especially for Koror and Yap. High Surf and Small Craft Advisories
are in effect for Koror. TS Kai-Tak is nearly stationary northwest
of Koror and a monsoon trough curves between Yap and Koror to a
circulation southwest of Chuuk at 3N150E; Invest Area 97W. Also,
fresh to strong southwest to west winds and heavy showers surged
across Palau this afternoon. Models differ significantly on the
development and movement of 97W. The current forecast is based on
the circulation moving slowly toward west or west-northwest and
gradually developing further over the weekend. The situation will
need to be monitored carefully. Fairly dry weather is arriving at
Chuuk for the near term, but fresh to strong trade winds and a few
showers are expected to develop for Chuuk by early next week.


Marianas Waters...None.


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