NWS Guam wrote its last area forecast discussion before the first event at Nov 24, 9:30 AM UTC, 4 hours 30 minutes earlier.
Area forecast discussion, Nov 24, 9:30 AM UTC, 4 hours 30 minutes before
Area Forecast Discussion
National Weather Service Tiyan GU
730 PM ChST Thu Nov 24 2022
.Marianas Synopsis...
Mostly cloudy skies with scattered showers are seen over Guam and
Rota with partly cloudy skies and isolated showers over Tinian and
Saipan. Mostly moderate trade winds prevail across the region. Buoys
and altimetry show seas between 5 and 8 feet.
&&
.Discussion...
A tropical disturbance, Invest 99W, is moving through the region to
the south of Guam. A trough extends north-northeastward from the
circulation. Scattered showers are evident over Guam and Rota,
becoming numerous with scattered thunderstorms east of Guam coastal
waters. As the system continues to drift slowly westward, the
stronger convection to the east will filter in, resulting in numerous
showers across Guam and Rota, with decreasing showers northward.
This is expected to occur near midnight, during our diurnal maximum
for convection. With some weak upper-level divergence expected over
the area along with CIMMS MIMIC data showing a sharp increase in
PWATs expected to move into the region, increased thunderstorm
coverage to scattered around midnight as well. The main energy with
the trough is then expected to move west near morning, with showers
decreasing to scattered and lingering over the Marianas through
Friday afternoon. Then, the dry trade-wind pattern is expected to
return to the region, continuing through most of next week.
&&
.Marine...
Mainly moderate trade winds are expected to continue through the
weekend, becoming moderate to fresh early next week. Combined seas of
6 to 8 feet are expected to continue through Friday night, then
subside a bit through the weekend. The primary swell is a long period
north swell that will slowly subside over the weekend. This north
swell is producing surf of 7 to 9 feet along north and east facing
reefs, resulting in a high surf advisory for north facing reefs and a
high risk of rip currents along north and east facing reefs. By
Sunday, the north swell will subside a bit, with the trade-wind swell
again becoming the dominant swell. Altimetry data does show seas of
around 10 feet moving toward the waters. Seas are not expected to
increase, however, as this swell is expected to subside a bit, though
seas of 10 feet are possible over the eastern waters late in the
weekend.
&&
.Tropical systems...
Two significant features remain over the region this evening. The
first is a weak circulation, JTWC Invest 99W, centered near 10N144E.
This system continues to slowly drift westward, with an associated
trough extending toward the north-northeast. Latest model guidance
shows little to no development as 99W moves away from the region.
The second system, JTWC Invest 90W, is centered near 9N163E. Latest
model guidance shows this system moving westward over the next few
days, following a track south of 99W. Models show little development
in 90W until it moves into western Micronesia. Then, both the GFS and
ECMWF shows a little development, with the ECMWF being the most
aggressive. Models currently keep 90W at or below tropical
Depression strength as it moves through Palau early to mid week next
week.
&&
.Eastern Micronesia...
The ITCZ is seen stretched across Pohnpei and Majuro and north of
Kosrae. Satellite shows increasing showers near Pohnpei with Invest
90W directly overhead, so decided to upgrade Pohnpei's forecast for
numerous showers tonight. Low end scattered showers are in store for
Majuro and Kosrae then will see an increase in showers for Kosrae as
the ITCZ pushes south. For Majuro, a surface trough is expected to
bring an increase in showers Friday night into Saturday. Then by
next week Monday, the ITCZ is forecast to dissipate.
Combined seas are about 4 to 6 ft for Kosrae and Pohnpei. For Majuro,
combined seas are slightly higher at 6 to 8 ft, but we should see sea
heights decrease a little bit over the next day or two.
&&
.Western Micronesia...
Fair weather this evening for Palau and Yap, then as 99W approaches
expect scattered showers. Both the GFS and the ECMWF take 99W
slightly south so there is a chance we may see an increase in shower
activity more than currently forecast. ASCAT showed a small area of
25 kt winds on the east side of the circulation so there may be
stronger winds and gusts if this system continues to develop. For
Chuuk, scattered showers tonight will increase as 90W tracks through,
then we should see stronger winds after 90W passes.
Last few model runs of the GFS, ECMWF, and the GFS Ensemble showed
consistency in 90W approaching Koror and Yap around Tuesday. For
now the models maintain it as a weak circulation with maybe around
20kts of wind. Will continue to monitor and see how the models
handle this system.
Expect building north swell to 4 ft the next day or two for Chuuk.
For Koror and Yap, long period swell is more north-northeast and we
may see up to 6 ft at Yap. Based off the swell heights, surf heights
are expected to be just below the 9 ft advisory criteria, but it's
possible to get a few surges of higher swell like we did for the
Marianas, which resulted in issuance of a high surf advisory.
&&
.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through late Friday night for GUZ001.
High Surf Advisory until 5 AM ChST Saturday for GUZ001.
MP...High Rip Current Risk through late Friday night for MPZ001>003.
High Surf Advisory until 5 AM ChST Saturday for MPZ001>003.
Marianas Waters...None.
&&
Marianas: Kelly/Kleeschulte
Micronesia: Hong