151
FXPQ50 PGUM 230609
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
409 PM ChST Mon Sep 23 2024

.Marianas Synopsis...
Satellite observations show decaying cirrus giving way to mid-level
stratocumulus. Ritidian and Tanapag buoys show combined seas of 2 to
4 feet across the Marianas.

&&

.Discussion...
Not much has changed with this forecast package. Current thinking is
that occasional rounds of heavy showers will be possible over the
next fews days with breaks inbetween. This is not too dissimilar
with what was seen earlier this morning. As Invest 91W lifts
northwest out of the Marianas towards the end of the week, a
southerly surge in winds and moisture could lead to an increase in
showers. Please see the Tropical systems section for updates on
Invest 91W and continue to monitor forecasts for updates.

&&

.Marine...
Marine conditions look to remain benign for much of the week. As
Invest 91W moves near the Marianas this week winds look to fall into
the light to gentle range. Without a significant fetch in winds,
seas look to remain in the 2 to 4 foot range through the first half
of the week. As Invest 91W pulls away from the Marianas, a large
fetch of southerly moderate to fresh winds will be possible. This
should allow seas to rise towards the end of the week. The forecast
for Invest 91W is to remain weak through the Marianas with little
impacts across the coastal waters. Significant changes in 91W`s
forecast would lead to significant changes in the marine forecast.
Continue to monitor forecasts for future updates.

&&

.Tropical systems...
JTWC`s Invest 91W continues to meander east of the Marianas as an
elongated, disorganized surface circulation, centered near 15N150E.
Recent convective trends have favored the southeastern portions of
the circulation. This system continues to be weak and highly
disorganized, but will continue to bring sporadic bursts of showers
and thunderstorms over and near the Marianas for the next few days as
the center gradually shifts westward. Model guidance indicates the
lopsided circulation may begin to nudge over the Marianas by Tuesday
night and pass west of the islands sometime Thursday. Convergent
southerly flow along the back side of the circulation may bring an
especially wet latter half of the week to the Marianas, and moderate
to occasionally fresh winds.

&&

.Eastern Micronesia...
A benign and dry pattern persists for the region, though at Pohnpei,
light winds allowed for showers and thunderstorms to develop over the
island. A broad surface trough is passing over the Marshalls but is
largely quiet, regarding showers and thunderstorms. In the short
term, have added a couple tweaks. First, have added a small uptick
in showers at Kosrae for late tonight and early morning, based on
computer models indicating a weak surface trough passing by in the
early morning hours. Secondly, with models showing a very light wind
pattern for the region the next few days, have proceeded with bumping
up Pohnpei and Kosrae Tuesday afternoon clouds and POPs, along with
a slight chance of thunderstorms in anticipation of some island-based
daytime convection. Heading into the late week, winds will remain
light to gentle and mostly variable in direction before a gentle
easterly flow resumes by the weekend. At this point, models depict a
weak ITCZ pattern taking shape.

No marine hazards are expected through the week. Seas are expected to
stay between 3 and 4 feet, composed of a mix of easterly and
southeasterly swell. Over the weekend, southeast swell may increase a
foot or 2 for Pohnpei and Kosrae.

&&

.Western Micronesia...
A broad west-southwest to east-northeast oriented trough remains
over far western Micronesia, winding just south of the Marianas and
extending through JTWC`s Invest 91W near 15N150E. Satellite shows
bands of heavy showers with embedded thunderstorms to the west and
northwest of Palau, and over Yap, roughly focused along the trough`s
axis. Further east, numerous showers and isolated thunderstorms are
seen to the north of Chuuk State, driven by low-level convergent flow
into 91W to the north and supported by strong divergence aloft.
Showers are moving west and away from Palau, but continue over Yap
this afternoon as the southwesterly flow south of Yap converges with
northeasterly flow out of 91W. POPs have been adjusted upward for Yap
tonight but remain at isolated further south near Palau. The
monsoon-like trough extending through Invest 91W will shift
northward over the next few days, bringing gentle to moderate
southwest to west flow over Palau and Yap by mid-week. The associated
convergence and moisture will bring on-and-off scattered showers for
the latter half of the week, mainly for Yap. To the east, Chuuk sits
along the northern edge of a large surface anticyclone, under a
swath of upper- level cloud debris from heavy showers moving away to
the north. Chuuk will remain fairly dry through the mid-week, with a
slight increase in showers for the latter half of the week due to an
approaching trade-wind trough.

Benign marine conditions continue. Babeldaob buoy data shows 1 to 3
ft seas near Palau, and altimetry data shows 2 to 4 ft seas just east
of Yap. Light to gentle winds are expected throughout the week, with
no marine hazards anticipated.

&&

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

$$

Marianas: Williams
Micronesia: Aydlett/DeCou