843
FXPQ50 PGUM 240756
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
556 PM ChST Tue Sep 24 2024

.Marianas Synopsis...
Satellite observations show mostly cloudy skies over the Marianas
with isolated brief thunderstorms popping up over Rota, Tinian and
Saipan coastal waters. A complex of numerous showers and scattered
thunderstorms is approaching the Marianas from just east of coastal
waters. Ritidian and Tanapag buoys show combined seas of 2 to 4 feet
across the Marianas.

&&

.Discussion...
Current forecast thinking is that occasional rounds of heavy showers
and thunderstorms will continue over and near the Marianas for the
next few days, with locally heavy rainfall possible as Invest 91W`s
circulation center crosses the islands. The center looks to nudge
over Saipan and Tinian beginning late tonight into early Wednesday
morning, but there is uncertainty with how long 91W will linger over
the Marianas before moving west or northwest. With the disorganized,
sporadic nature of this system, there is plenty of uncertainty with
the location and timing of showers. Shower chances look to increase
for Thursday and Friday with a convergent southerly flow setting up
over the islands behind 91W. Winds don`t look particularly impressive
with this system with gentle to moderate speeds expected, becoming
fresh at times with a few convectively- driven strong gusts possible.
Please refer to the Tropical Systems section for more on Invest 91W
and continue to monitor forecasts for updates.

&&

.Marine...
Wind direction is shifting with the approach of JTWC`s Invest 91W,
which is expected to move over the Marianas late overnight through
Wednesday morning. Winds will remain west to southwest for Guam and
Rota tonight and the next few days, but northeasterly to easterly
winds are in the forecast for Tinian and Saipan through Wednesday,
as model guidance places the center of circulation just south of and
over Tinian as it crosses the islands. Winds are still expected to
remain light to moderate over the coming days with occasional fresh
gusts. As the circulation crosses the islands, expect increased
shower and thunderstorm chances over coastal waters. Showers may be
locally heavy at times and a few strong convectively-driven gusts
will be possible. Seas look to remain between 3 and 5 feet through
much of the week.

&&

.Tropical Systems... JTWC`s Invest 91W remains weak and disorganized
as it meanders west toward the Marianas, with the circulation center
now located near 15N147E, roughly 100 miles east of Saipan. Latest
satellite shows numerous showers and scattered thunderstorms along
the system`s eastern and southern flanks wrapping into the center,
with showers spread far to the southeast, just north of Chuuk State.
The strongest convection is organized loosely along a northwest to
southeast oriented line south of the circulation center, which looks
to be moving west- southwest toward Guam and Rota. This system will
continue to bring sporadic bursts of heavy showers and thunderstorms
over and near the Marianas for the next few days along with moderate
to occasionally fresh winds. A few strong convectively- driven gusts
will be possible. The circulation is expected to move over the
islands late tonight through early Wednesday morning, then gradually
move northwest of the CNMI on Thursday and Friday. Shower chances
will increase for the Marianas on Thursday through Saturday as
convergent southerly flow moves overhead behind the departing system.
91W will be closely monitored, but is not favored to develop
meaningfully in the coming days.

&&

.Eastern Micronesia...
Afternoon visible satellite imagery shows very quiet conditions
across the region. Showers and thunderstorms had developed near
Kosrae today with a shallow trough and short-lived circulation just
to the north, but all convection has ceased in the past hour. As
noted the past few forecast cycles, the week is still set to be quite
dry with gentle winds. Subtle troughs and other weak surface
features will cause wind directions to fluctuate, so will maintain
light and variable winds for portions of the forecasts for all 3
areas. Over the weekend, models still show weak trade-wind
convergence setting up across Kosrae and the Marshalls that will
bring increasing showers and a slight boost in easterly winds.

Little has changed regarding marine conditions as seas are still
expected to hover between 3 and 4 feet, a mix of east and southeast
swell and a small northerly swell. As noted yesterday, southeasterly
swell will increase a foot or 2 over the weekend.

&&

.Western Micronesia...
A monsoon-like trough extends north of Palau, through a disturbance
north of Yap near 13N137E, and ending at another disturbance east of
the Marianas, known as Invest 91W. Convergent west-southwesterlies
south of these features remain the focus of showery weather for most
of the region, however Chuuk is more influenced by a weak ridge
tucked to the south of the convergent flow into 91W. As these
features slowly push northwest, convergent west-southwesterlies keep
scattered showers around in far western Micronesia over the next
several days, more so for Yap due to the proximity. For Chuuk,
relatively quiet conditions begin to change Thursday as the ridge
pushes off the west and off-and-on trade showers return. The ridge
reaches Palau and Yap over the weekend, providing a brief lull in
showers, also followed by a transition to a trade-wind pattern next
week.

Benign marine conditions continue. Babeldaob buoy data shows seas
around 2 ft seas near Palau, and altimetry data shows 2 to 4 ft seas
just east of Chuuk. 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: Decou
East Micronesia: Aydlett
West Micronesia: Cruz