Flash Flood Warning 5, NWS Guam

Area Forecast Discussion
National Weather Service Tiyan GU
1222 PM ChST Tue Aug 24 2021

.Update...
Updated all zones in the Marianas with an increase in
chance of rain to 60 percent. As the trough of low pressure
previously over the Marianas drifted to the northwest, the showers
and thunderstorms filled in this morning to cover the entire
Marianas. Looks like this will remain for the rest of the day and
the forecast will be updated with the next schedule issuance at
4PM, if not earlier.

&&

.Prev discussion... /issued 758 AM ChST Tue Aug 24 2021/

Marianas Synopsis...
Light and variable to light southeast winds prevail over the
Marianas as a surface trough slowly moves west. Radar and satellite
indicate showers and thunderstorms just west of Tinian and Saipan's
coastal waters.

Discussion...
Showers and thunderstorms were persistent just west of Tinian's
coastal waters all last night. Today's forecast calls for an
increase in showers and thunderstorms for Tinian and Saipan, and
thinning out by this afternoon. Also it looks like Guam and Rota may
see an increase in clouds and showers as well, but kept them partly
cloudy with isolated showers as it seems there is a lack of deep
convective clouds nearby. Still have the chance of island effect
thunderstorms for Guam today as we are expecting less cloud cover
compared to yesterday.

Also looks like a day for increased showers for Thursday, but pushing
through faster and ending sooner than previously forecast. Went with
isolated showers for Thursday with a surface trough passing through,
but with an upper low nearby to add vertical lift and instability,
may go back to scattered fr Thursday, and maybe Friday.

Combined seas will be at 2 to 3 feet for the remainder of the week.

Eastern Micronesia...
All of the convection seems to have collapsed at once in Eastern
Micronesia, which necessitated some pretty big revisions to the
forecast. The trough that was affecting Pohnpei has moved far enough
away that even Chuuk is nearing the back edge of that activity. So,
through Wednesday night, isolated showers for everyone. Majuro could
go scattered on Thursday, depending on what the nascent ITCZ east of
them ends up doing. The GFS seems to favor it, so went ahead and
put scattered showers and isolated thunderstorms in for everyone
Friday and Saturday. Until then, enjoy the somewhat drier weather.

Benign marine conditions remain the rule in Eastern Micronesia for
this week at least, and a good chance for next week as well. With
winds of 15 knots or less, and seas of 4 feet or less, the only
weather related hazard for mariners is lightning near thunderstorms.

Western Micronesia...
A surface trough of low pressure has moved west of Chuuk, and Chuuk
is now nearing the eastern edge of the weather. Retained scattered
showers for the morning, then the weather dries out a little, with
the next round of scattered showers being Thursday and Friday. Koror
and Yap are a bit drier, with Koror being dry this morning until
Thursday. Then, by Friday, it dries out again. Meanwhile, Yap will
stay relatively dry through the entire forecast period.

Benign marine conditions are even more the rule in Western
Micronesia. Seas will be 3 feet or less at Chuuk, and 2 feet or less
at Yap and Koror. Winds will be 10 kt or less throughout Western
Micronesia. The only weather related hazard for mariners will be,
once again, lightning near thunderstorms.

&&

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

Marianas: Doll/Mcfarland/Edson/Schank