Area Forecast Discussion
Issued by NWS Tiyan, Guam

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FXPQ50 PGUM 240840

Area Forecast Discussion
National Weather Service Tiyan GU
640 PM ChST Thu Jun 24 2021

.Marianas Synopsis...
Light winds winds and isolated showers and thunderstorms prevail over
the Marianas this afternoon. Buoy data show combined seas of 2 to 3

Small changes made to the forecast. A few thunderstorms formed west
of Guam this afternoon. Satellite imagery showed a isolated Cbs over
the area. Even though this activity seems to be waning felt another
thunderstorm or two is possible tonight. Models keep things fairly
dry the next few days with deep-layer moisture lacking and only
isolated showers expected Friday though Saturday night. A slight
increase in deep-layer moisture will cause mostly cloudy skies,
isolated showers and thunderstorms Sunday through Tuesday. A
circulation forming to the southeast of Guam is predicted to cause a
chance of showers and thunderstorms by next Thursday.


Combined seas are currently 2 to 3 feet and models project this to
slowly build a couple of feet over the next week. Primary swell is
from the east at 2 to 3 feet and slowly builds to 3 to 4 feet by
Tuesday. A slightly weaker west to northwest swell continues to be
generated from the retreating TS Champi, until it subsides by
Monday. These gentle swells have generated modest surf heights of 2
to 4 feet for all reefs except for south facing reefs, with only 1 to
3 feet surf. Rip current risk remains low for these sea conditions.


.Eastern Micronesia and Chuuk...
A trough is located just south of Chuuk and Pohnpei and is producing
scattered showers and isolated thunderstorms. This trough looks to
stay south of the islands, but cloud cover should remain high
overnight. The rest of the region is quiet with mostly clear to
partly cloudy skies.

A dry trade-wind pattern is in place from the dateline to Kosrae
State. These dry trade winds are helping to stabilize the atmosphere
as it is bringing warm, dry air to the mid layers of the atmosphere.
Friday night, the trade winds will go from stabilizing to de-
stabilizing as convergence will cause a new ITCZ to form. The ECMWF,
NAVGEM, and GFS still point towards this ITCZ event being fragmented
or poorly defined, with a series of weak trade-wind troughs
enhancing convection. Based on these factors, the start of next week
is shaping up to be wet across much of the region. The long term
forecast was adjusted to reflect this wetting trend, with more
showers and thunderstorms added to the forecast.

A weak trade-wind swell will keep combined seas between 5 and 7 feet
for the Marshalls. Seas at Chuuk, Pohnpei, and Kosrae will be around
3 and 5 feet.


.Western Micronesia for Yap and Palau...
A weak ridge is keeping skies mostly clear for the region. These
calm conditions look to continue through the weekend, as the ridge
stays in place. There is a slight chance for island effect
thunderstorms Friday afternoon at Koror. The main limiting factor to
thunderstorms will be the dry air in the mid-level of the

Through the weekend, both Yap and Koror can expect calm conditions.
The weather pattern beings to change on Monday, as a series of weak
troughs move into the region. These troughs, from Chuuk, are not
well forecasted as they change from model to model and run to run.
Even though they are poorly defined, troughs are still expected to
move into the region. Because of the troughs, the forecast was
updated to include more showers and thunderstorms at the start of
the week.

Sea conditions for Yap and Palau are favorable with seas between 2
and 3 feet.

Marianas Waters...None.


Marianas: Ziobro/Cruz
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