Area Forecast Discussion
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FXPQ60 PGUM 222032

Area Forecast Discussion
National Weather Service Tiyan GU
630 AM ChST Fri Jun 23 2017

.Marianas Synopsis...
Partly cloudy skies with isolated showers and gentle to moderate
trade winds prevail across the Marianas. An upper-level low is
seen on water vapor imagery to the northeast of Saipan. A
pronounced tropical disturbance is present to the east-southeast
of Guam.


An upper-level low/TUTT cell is approaching the Marianas from the
northeast while a pronounced tropical disturbance is approaching
from the east-southeast. As the trough and low approach, isolated
thunderstorms are expected to move into the region later tonight.
On Saturday, as the surface trough and upper-level low begin to
interact over the islands, shower coverage is likely to increase
to scattered with deep convection more likely as well. By the
beginning of next week, these systems will move west of the
Marianas, allowing a drier trade-wind regime to move back over the

By the middle of the week, another weak disturbance will approach
the islands. Time/heights products show an increase in deep layer
moisture Wednesday and Thursday. Therefore, decided to introduce
isolated thunderstorms to the forecast for that time period while
maintaining isolated showers, for now. Scattered showers are a
possibility as well, but a little too early to increase to
scattered at this time.


.Eastern Micronesia...
Significant debris cloudiness remains over Eastern Micronesia.
Upped the sky cover at Majuro and Kosrae from Partly cloudy to
Partly sunny. After today the clouds should break up a bit until
the next disturbance, which will emerge Saturday for Kosrae and
on Sunday for Majuro and Pohnpei. Had thought the clouds would
move past Pohnpei early on and allow a clearer area to move over,
so left the forecast Partly cloudy there. Unfortunately this
doesn`t seem to have happened, perhaps Pohnpei should have been
Partly sunny today as well. Wind and wave conditions are expected
to remain benign through the forecast period. The PacIOOS
inundation forecast for Majuro shows them just reaching the red
line. With the sea heights being rather subdued this must be
primarily tidal driven. Majuro has reached these heights before
and it wasn`t a big deal, at this point expect a repeat of that
from this rather marginal event.


.Western Micronesia...
The disturbance which had affected Pohnpei began moving west-
northwestward versus westward. This is allowing it to miss Chuuk.
Chuuk is expected to remain Partly cloudy until Saturday night
when the disturbance from Eastern Micronesia could start to affect
them too. The disturbance currently south of Yap will continue to
affect them with Isolated showers and thunderstorms. The scattered
showers are expected to pass south of them on their way to Palau.
After tonight, the weather at Yap will begin an improving trend
which will persist through the remainder of the forecast period.
Koror is expected to have the heaviest weather today. A massive
complex of showers and thunderstorms is moving right toward them,
so upped their forecast to scattered showers and isolated
thunderstorms. Mostly, the winds will be light and variable.
However, noticed on the 12Z sounding at Koror that there is up to
24 knots of wind at 10 thousand feet and up to 32 knots of wind
at 15 thousand feet. Went ahead and put gusts up to 20 knots near
thunderstorms in case they can bring some of those high wind
speeds down to the surface. Otherwise, winds and seas will be
benign, with a possibility of just 1 to 2 feet at Koror by


Marianas Waters...None.


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