Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 242142
Area Forecast Discussion
National Weather Service Tiyan GU
540 AM ChST Sun Sep 25 2016
.Synopsis...Isolated showers and northeast winds prevail across
the Marianas this morning.
A weak ridge of high pressure was located just to the west of
the Marianas. Northeast winds will become east during the day.
This will be temporary as a weak surface trough pushing in from
the east will cause winds to become northeast tonight.
This weak surface trough will generate isolated showers and
thunderstorms today and tonight.
Another surface trough could be found north of Pohnpei this
morning. This trough will move westward and by Monday a
circulation will form on it. Models agree on the circulation
moving just north of Saipan the second half of the week. Northeast
winds Monday and Tuesday will become Northwest Wednesday as the
circulation enters the area. Still not certain on shower coverage
with this feature...but feel that it will at least generate some
clouds and thunderstorms. Added mostly cloudy skies and isolated
thunderstorms to the forecast for Tuesday night through Friday.
Buoy data show seas between 3 to 4 feet this morning. A east
swell of 3 to 5 feet is expected today will decrease to 3 to 4
feet tonight. Surf of 4 to 6 feet on east facing reefs with 2 to 4
feet on south and north facing reefs are expected today. Ritidian
buoy did show a swell from the west-southwest so kept surf on west
facing reefs at 1 to 3 feet. Little change is expected through at
Gentle to moderate trade winds are found from Chuuk State eastward
to the Marshall Islands. A surface trough is visible near Chuuk and
another one is approaching Majuro this morning. Thunderstorms with
locally heavy showers associated with the first trough will persist
near Chuuk thru this evening. Sporadic showers and possible
thunderstorms related to the second trough will also accompany
Majuro thru tonight. Situated in between these two systems, fair
weather should prevail near Pohnpei and Kosrae thru Monday
afternoon. This same area of fair weather is also expected to shift
over Chuuk by Monday.
After passing across the Marshall Islands on Monday, the second
system will gradually make its way westward. As a result, anticipate
wet weather to arrive at Kosrae and Pohnpei by Monday night, and
possible Chuuk again near midweek.
Discussion on the Chuuk forecast is included in the Eastern
Micronesia section above.
Newly upgraded Typhoon Megi over the Philippine Sea near 19N133E is
steadily pulling west-northwest this morning. This has allowed
pockets of deep convection near the convergent band of southwest
winds to shift northwest of Koror and Yap. A few lingering showers
and thunderstorms are still possible today but a surface ridge to
the east should usher in drier air starting this evening. Toward
midweek, the threat of thunderstorms will return as an upper-level
trough moves over the region.