Area Forecast Discussion
Issued by NWS Tiyan, Guam

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FXPQ50 PGUM 252213

Area Forecast Discussion
National Weather Service Tiyan GU
813 AM ChST Thu May 26 2022

.Marianas Synopsis...
Guam Doppler weather radar shows only a few showers within the
Marianas waters. A weakening cluster of showers is seen southwest of
the Guam waters. The buoys report combined seas of 3 to 5 feet,
composed mainly of east-northeast swell and southeast wind waves.


A dry trade-wind regime remains in place over the Marianas, although
the deep tropical moisture is getting closer. Last night, thanks to
the TUTT, we had some showers and thunderstorms just south of the
Guam waters. Those are fading in a hurry now, leaving us in the dry
weather again as the TUTT weakens.

The models are still trying to gin up some moisture from the ITCZ, it
now looks like it might arrive somewhat Monday but more so Tuesday.
Will it get delayed again? That`s starting to seem somewhat likely.
Wet season will bring it at some point; eventually the model will be
correct. How many times will it try to call it before then, that`s
the question.


Combined seas of 3 to 5 feet last night are subsiding to between 2
and 4 feet today. The seas will remain reduced through Friday night,
then will briefly bob up to between 3 and 5 feet, then diminish back
to between 2 and 4 feet Saturday night. Seas could even sink further
to between 1 and 3 feet early next month. Marine conditions are
benign and could grow even a little more so over the next week.


.Fire weather...
The brief passing showers of last night did not add up to a wetting
rain, so the KBDI continues its renewed rise. It is now up to 665.
Winds will be mostly light to gentle through the end of the month, so
no fire weather watches or red flag warnings are expected. Wet season
is on the way, but isn`t here yet.


.Tropical systems...
Invest Area 92W, which was west of Koror, has been closed. This area
is no longer judged to be in need of special monitoring.


.Eastern Micronesia and Chuuk...
The ITCZ extends from the dateline to Chuuk state. Troughs embedded
in the ITCZ are creating extensive showers and several

The main change to the forecast was the addition of categorical
showers for Kosrae. This morning, a segment of the ITCZ has set up
just south of Kosrae. While the heaviest showers remain south of the
coastal waters, they are moving northward, toward the island. Other
than the near term change to the forecast, the bulk of the forecast
remains unchanged. In general, the main synoptic forces remain in
place from the previous forecast. With low-level convergence because
of the ITCZ and convection being enhanced by embedded troughs.
Finally, an upper-level low near 12N146E is enhancing divergence
aloft. The recent trend of the GFS has been to downgrade the extent
of the ITCZ. This downward trend is not seen in the ECMWF or the
NAVGEM but instead they keep convection more widespread. For now the
long term forecast is mostly unchanged but if the other models
follow the GFS trend then the forecast will follow suit.

The marine forecast remains unchanged, with mainly gentle to
occasionally moderate winds area-wide. Seas are currently 3 to 5
feet. The most recent ASCAT pass does show a large area of 20 knot
winds across the dateline. As the wind field expands, this fetch
will cause a slight increase of winds.


.Western Micronesia for Yap and Palau...
Invest 92W continues to slowly move westward. Reports from Palau last
night showed gusty winds with a gust of 35 knots reported at the
rock island weather station.

In the short term, Palau will see an improvement as invest 92W moves
towards 130E. At Yap conditions will deteriorate as the edge of the
ITCZ moves closer to the island. This could bring heavy rain to Yap
later today and tonight however, over the next 24 hours, rainfall
estimates, for Yap, are around 1 inch. Through the weekend the
weather will start to dry out with less convection in the region.
Around Friday, models show the edge of the ITCZ breaking off. The
GFS, ECMWF, and NAVGEM all show a circulation begin to form and
models expect the system to slowly move northward. The forecast for
the next week depends heavily on the movement and development of the
system. For now the forecast leans towards a wetter forecast with
showers and thunderstorms possible through the middle of next week.

Seas and winds remain the same as the previous few days, with winds
of 5 to 10 knots and seas of 3 to 4 feet. Stronger gusts are
possible close to showers.


Marianas Waters...None.


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