Area Forecast Discussion
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FXPQ60 PGUM 250837

Area Forecast Discussion
National Weather Service Tiyan GU
538 PM ChST Mon Sep 25 2017

.Marianas Synopsis...
A westward moving surface trough and favorable winds aloft combined
to bring abundant showers and thunderstorms to much of the Marianas
this afternoon. An upper-level anticyclone to the west and an upper-
level low to the east generated strong north winds aloft that induced
sufficient rising motion in the atmosphere to sustain today`s deep
convection. A few thunderstorms developed west of Agat that put off
an impressive amount of lightning.

Radar imagery shows scattered showers still moving through the area
waters, mainly west of the islands. Infrared satellite imagery shows
confirms that the bulk of deep convection has passed to the west and
continues to move away.

Well to the east, the upper-level low, near 17N152E, and a surface
trough are generating scattered showers and thunderstorms well north
of Chuuk and Pohnpei.


After an active weather day, conditions will quiet down this evening
with clouds breaking up later tonight. More showers and thunderstorms
are expected later on Tuesday as the surface trough to the east
approaches the area. At the same time, the upper-low will also drift
westward maintaining favorable winds aloft to generate thunderstorms.

By Wednesday, winds will weaken, becoming light and variable for the
latter half of the week. Although models show less moisture in the
area then, such light winds could permit some island convection
during the afternoon hours.


Seas picked up a little bit today to between 5 and 6 feet as the
gusty showers moved through, but winds have since decreased. Seas
have fallen to between 3 and 5 feet and are expected to remain in
this range through Tuesday night, then decrease another foot on


.Eastern Micronesia...
A surface trough extends across eastern Micronesia from 2N160E to
8N180. This trough will bring scattered showers and isolated
thunderstorms to Kosrae and Majuro tonight. The trough will move
westward but weaken as it goes, although enough activity will
persist to bring mostly cloudy skies, isolated showers and
thunderstorm Tuesday night and Wednesday. Another surface trough
will develop across eastern Micronesia the second half of the week
bringing scattered showers and isolated thunderstorms over Kosrae
Friday and Saturday. This same trough will bring mostly cloudy
skies, isolated showers and thunderstorms to Majuro Thursday
through Saturday.


.Western Micronesia...
Low-level wind flow convergence along the edge of a ridge of high
pressure will keep isolated showers and thunderstorms over Palau
and Yap tonight. A surface trough could be found south of Chuuk
this afternoon. The trough will move west and northwest and bring
scattered showers and isolated thunderstorms to Yap and Palau
Tuesday. The scattered showers will persist across Palau through
Tuesday night. Low-level convergence east of the trough will cause
scattered showers and isolated thunderstorms to develop over
Chuuk Tuesday night. Lingering convergence will generate isolated
showers and thunderstorms at Palau Wednesday and Wednesday night.

Models show a second trough developing south of Chuuk Wednesday and
moving slowly northwestward. This will cause more isolated showers
and thunderstorms at Chuuk Wednesday night through Friday.


Marianas Waters...None.


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