Area Forecast Discussion
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FXPQ60 PGUM 280551

Area Forecast Discussion
National Weather Service Tiyan GU
351 PM ChST Wed Sep 28 2016

Tropical Depression Chaba (21W) will move through the Marianas
tonight with gusty winds, heavy rain and lots of lightning.


GFS is handling Chaba fairly well track-wise, and was able to use
its winds for tonight and Thursday, after bumping up wind speed a
little. The center of Chaba should pass over or near Rota around
2 or 3 AM tonight. But the main issue is rainfall, with 4 to
8 inches possible tonight and Thursday. Chaba has been producing
a long series of strong thunderstorm outbreaks the last 1-2 days,
and is still doing so this afternoon. If an outbreak fires up
over one of the islands, several inches of rain could fall in a
short time, and as a result have issued a flood advisory through
Thursday. Conditions should improve somewhat Thursday night and
Friday, and showers should become isolated aound Friday evening.


Continued the Small Craft and High Surf Advisories, as seas should
still hit 10 ft in northern Saipan waters. High surf is currently
confined to Tinian and saipan, but it may need to be extended to
Guam and Rota if Chaba intensifies unexpectedly.


.Tropical systems...
TD Chaba is still not well-organized, as competing convective
outbreaks keep the system from consolidating. This should keep it
from intensifying much overnight, though it could reach low-end
tropical storm early Thursday morning. The highest winds, 25-30 kt,
are north of the center, with only 15-20 kt south of the center.
Chaba is still putting out plenty of lightning with each new
outbreak of convection, which could make for a stormy night for
the Marianas. Rainfall will depend a lot on where the outbreaks
take place, with up to 8 inches possible under the heaviest ones.
With the center expected to pass near or over Rota during the
early morning hours, the highest winds should be over Tinian and


.Eastern Micronesia...
A trade-wind trough accompanied by a large area of showers is moving
westward from the Marshall Islands into Kosrae State this afternoon.
Also, extensive clouds along patchy showers and a few thunderstorms
covers much of the area north of Pohnpei and Kosrae to Wake Island.
Models indicate the trough will continue to move west across the
region, with showery weather for Majuro through tonight at least,
Kosrae through Friday night, Pohnpei by Friday through Saturday, and
Chuuk by Friday or Saturday. Relatively dry weather is expected to
follow behind the trough.

Benign sea conditions are expected at Majuro the next several days.
However, PACIOOS Wave Run-Up Forecast shows higher seas late this
week through weekend with the New Moon phase. Water levels will be
high during high tides from September 29 through October 3.
Inundation is not expected at this time as combined seas will be
between 3 and 5 feet. Majuro/Kalo Buoy shows combined seas around 3


.Western Micronesia...
Light winds and just a few showers are seen across Yap and Palau
today. Tropical Depression Chaba (21W) will pass toward the west-
northwest across the Marianas overnight and GFS Model keeps Chaba
well north of Yap on Friday with the bulk heavier showers mainly
north of 10N. Surface winds will become southwest and moist across
far Western Micronesia Thursday through Friday. Another disturbance
will approach from the east early next week with increased clouds
and showers again.

Moderate long-period northwest swell produced by distant Typhoon
Megi, now over China, will cause higher seas and surf across The
Republic of Palau and Yap State the next couple of days. However,
both seas and surf should remain below hazardous levels.


GU...Flood Watch through Thursday evening for GUZ001>004.

     Tropical Storm Watch for GUZ001>004.

     High Surf Advisory until 6 PM CHST Thursday for GUZ003-004.

Marianas Waters...Tropical Storm Watch for PMZ151>154.

     Small Craft Advisory until 6 PM CHST Thursday for PMZ151>154.



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