Area Forecast Discussion
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FXPQ60 PGUM 220919

Area Forecast Discussion
National Weather Service Tiyan GU
600 PM ChST Sat Jul 22 2017

.Marianas Synopsis...
Radar and satellite show isolated showers and thunderstorms across
the Marianas, with the greatest concentration near Tinian and Saipan
and south of Guam. High cirrus clouds are streaming northward across
the region from deep convection south of Guam between 9N and 12N.
Trade winds have become gentle, and seas at the buoys are generally
between 3 and 4 ft.


The forecast is basically the same as previous, except have brought
in mostly cloudy skies and isolated thunderstorms this evening.
Models show trade winds collapsing over the next day or two as a
monsoon trough developing out west and northwest of the Marianas
turns our winds to southeast Sunday, south on Monday, and finally
to southwest by Thursday. While that often means showery weather
for the Marianas, in this case the trough will be setting up far
enough to the northwest to bring the dry ridge south of the trough
into the region. Thus, after mostly cloudy with isolated showers
and thunderstorms the next couple of days, drier conditions with
partly cloudy skies and isolated showers should set in by Tuesday
and persist through next weekend.


Seas should remain generally at 3-5 ft the next week or so. But the
shift from a trade-wind regime to a monsoonal regime will cause the
east swell to slowly decrease later in the week while a minor
southwest swell comes in the last half of this week.


.Eastern Micronesia...
Trade-wind convergence produced an area of scattered showers and
isolated thunderstorms over the eastern half of Micronesia. This
afternoon, satellite imagery showed scattered showers and isolated
thunderstorms over Pohnpei and Kosrae. Expect the scattered showers
and isolated thunderstorms to persist at Kosrae tonight. As the
area moves west, scattered showers and isolated thunderstorms will
develop over Pohnpei tonight and continue through Sunday. Another
area of trade-wind convergence will bring scattered showers and
isolated thunderstorms to Majuro Sunday night, and to Kosrae Monday
through Tuesday.


.Western Micronesia...
The main weather feature over western Micronesia still is the
developing circulation west of Palau near 9N132E. It is expected to
develop further as it treks north of 10N during the next few days.
The circulation will not be a direct concern to Palau or Yap as it is
moving away from the area, but it will pull the monsoon trough
northward and cause a strengthening of the monsoon flow.

Showers were only isolated over Palau this afternoon but scattered
showers and isolated thunderstorms will build back across Palau
tonight. Convergence north of the monsoon trough will produce
scattered showers and isolated thunderstorms over Yap tonight.

As the circulation develops, it will increase monsoon flow over the
area, which will bring numerous showers and scattered thunderstorms
to Palau Sunday through Monday night. As periods of heavy rain are
expected at Palau, on-and-off flooding is likely. If the rainfall
is persistent than there is the possibility of mudslides in some

Winds of 15 to 20 knots are expected tonight and Sunday but will
likely increase to 15 to 25 knots with higher gusts Sunday night
through Monday night.

The increased monsoon flow will also cause an increase in seas of up
to 10 feet by Sunday night through Monday night at Palau and up to 9
feet at Yap. A southwest swell will gradually build through the
weekend. The southwest swell will increase surf on west, southwest,
and south facing reefs of these two islands. Across Palau and Yap
surf could briefly become hazardous sometime Sunday night through
Monday night.

The showers and thunderstorms that pushed across Chuuk this morning
have dissipated, and weak high pressure will build over the area
through Sunday. Trade-wind convergence will produce areas of
scattered showers and isolated thunderstorms just south of Chuuk
through much of the coming week. The bulk of the showers will
remain south of Chuuk but will be close enough to produce isolated
showers and thunderstorms Sunday night through Thursday.


Marianas Waters...None.



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