Area Forecast Discussion
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Area Forecast Discussion
National Weather Service Tiyan GU
700 PM ChST Mon Sep 26 2016

.Synopsis...
Isolated showers and light east to northeast winds are present
across the region, with seas near 4 feet at the buoys. The main
feature of interest is JTWC`s invest area 98W, a disturbance
about 900 miles east of the Marianas near 16N158E, moving west.

&&

.Discussion...
Based on latest models, have pushed back the period of scattered
showers 12 hours, now starting Wed morning and lasting through
Thursday night as 98W moves by. Otherwise, the basic forecast is
little changed. Confidence in winds is low, depending on how 98W
moves and on how much it develops. Neither the ECMWF nor the GFS
develop it very much at all, but its appearance on satellite
imagery suggests some potential for development.

&&

.Marine...
Have increased the west swell coming in from Typhoon Megi, peaking
at 4 feet on Thursday. This will result in surf up to 5 or 6 feet
Wed-Sat along west and north facing shores, with a moderate rip
risk.

&&

.Tropical systems...
GFS and ECMWF both keep 98W rather weak, suggesting it will not
even make a decent tropical depression, but satellite imagery
shows a partially exposed closed circulation on the north edge of
the cloud mass, with cycling deep convection firing up at
intervals. Winds at 50 kft are north at 25 kt or so, shearing the
convection south of the center, hindering significant development.
But ASCAT shows 25 kt winds in the northeast quadrant of the
circulation. With mixed signals for now, we will be keeping a
close eye on 98W.

&&

.Eastern Micronesia...
Relatively quiet weather is seen across the eastern region from
Chuuk to Majuro. A broad surface trough is generating showers and
thunderstorms from north of Kosrae to the northern Marshall Islands.
Spotty convection is seen ahead of this trough near Kosrae and
Pohnpei. This trough will slowly head west, with most of the
moisture expected to keep just north of the main islands as the
trough tries to link up with the tropical disturbance well north of
Pohnpei near 15N158E. Fair weather will build in at Majuro tonight
and continue at least through Tuesday afternoon. Another surface
trough will cross the date line late Tuesday and bring the next
round of showers to Majuro by Wednesday. Models show more moisture
with this trough as it passes over the islands, therefore maintained
the scattered showers for Majuro around midweek. Could see scattered
showers at Kosrae and Pohnpei later in the week, and at Chuuk by the
weekend.

&&

.Western Micronesia...
A weak ridge remains in place over Yap and Koror as Typhoon Megi
heads farther from the region on its approach to Taiwan. Southeast
to south winds at Yap and Koror will gradually shift to east and
then northeast as a weak surface trough approaches tonight and
Tuesday. Isolated showers and thunderstorms will persist in the
region tonight through Tuesday night. Winds will become light and
variable late Wednesday or Thursday as the tropical disturbance
north of Pohnpei approaches the Marianas. Models still show little
development with this disturbance, but it could pull up southwest
winds across Yap and Koror by the end of the week.

&&

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

&&

$$

Middlebrooke/M. Aydlett



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