Area Forecast Discussion
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FXPQ60 PGUM 231028

Area Forecast Discussion
National Weather Service Tiyan GU
827 PM ChST Sat Sep 23 2017

Showers seem to be increasing across the Guam and Rota
area. Updated shower coverage to scattered for the rest
of the night.


.Prev discussion... /issued 259 PM CHST Sat Sep 23 2017/

Marianas Synopsis...East winds and isolated showers and
thunderstorms prevail over the Marianas this afternoon.

A surface trough could be found on the afternoon analysis just east
of the Marianas. Satellite imagery shows scattered showers and
isolated thunderstorms east of the trough axis and east of 150E.
Models show the trough passing over the ares Sunday and Sunday night.
Showers will increase slightly from what is around the Marinas this
afternoon, but predominant coverage should remain isolated. Another
surface trough will follow quickly behind the first trough an extend
the possibility of isolated thunderstorms Monday and Monday night.

GFS is showing a circulation developing over the Marianas by
Wednesday night. ECMWF and NAVGEM do not show this but they do show
light winds over the Marianas Wednesday though Saturday. Not certain
about the circulation as other models and model runs did not show
feature. Models do hint at the possibility of a weak trough over the
local area and this could possibly generate isolated showers and
thunderstorms Wednesday night through Friday night.

Observations this afternoon from Ipan, Ritidian and Tanapag buoys
indicate sea heights between 4 to 5 feet. The buoys show the east
swell and Ritidian and Tanapag show a northeast swell.  Models show
that the east swell will persist through the forecast and the
northeast swell is predicted to remain until Monday. Since the east
swell has increased slightly the rip current risk has risen to
moderate levels on east facing reefs. This is temporary as models show
the seas and swell decreasing an the rip current risk will return to
low by Monday.

Eastern Micronesia...
Now that the surface trough has moved out of the region, generally
fair weather prevails. Trade wind convergence will bring mostly
cloudy skies and a few showers by Monday. Both Kosrae and Majuro
should see the fair weather return later in the week.

Western Micronesia...
A developing circulation near 5N141E is the major weather feature
in the region. At 2pm, a Special Weather Statement was issued to
provide a heads up for increased weather and possible hazardous seas
for Koror and Yap. Considered putting out a small craft advisory
but will wait a little longer to see if this system becomes
better organized. Models keep the circulation skirting south of
Koror through late Sunday.  Satellite shows an area of active
convection about 160 miles east of Koror propagating westward.
Already brought in the scattered showers and isolated
thunderstorms to Yap`s forecast tonight and to Palau by Sunday.
Some gusts in the showers are possible.

Chuuk remains south of the surface trough and much of the showers
and isolated thunderstorms have exited their region. Look for
another round of cloudy skies and showers from an approaching
surface trough by mid week.


Marianas Waters...None.


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