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FXPQ60 PGUM 290730

Area Forecast Discussion
National Weather Service Tiyan GU
509 PM ChST Thu Jun 29 2017

.Marianas Synopsis...Divergence from a deep upper-level trough
west of the Marianas is continuing to aid a wide spread area of
scattered to numerous shows to the east of the trough to as far
east as 148E. Thunderstorms and lightning have been observed
within this mass primarily to the west of the Marianas but also in
and out on a diurnal basis throughout the entire complex. Seas
remain relatively flat at 3 to 5 feet straight out of the east.
Satellite imagery shows the whole weather pattern slowly drifting
toward the west.


Rainfall had been heavy today over Guam with up to 1.85 inches so
far today. Satellite imagery shows that strongest showers have
been over Guam but all islands up through Saipan have had
significant precipitation (.65 inches reported today at the Saipan
airport). One can see breaks in the imagery, especially north of
Guam and well to the east. There has also  been less lightning
strikes reported during the afternoon than earlier, but this looks
to be expect another episode tonight throughout the
Marianas. Both the GFS and ECMWF have the most intense
precipitation lingering through tomorrow morning before break out
occurs from north to south. I kept everything isolated, including
the chance for thunderstorms on Friday, but might have to adjust
for Guam as the low level vorticity seems a little stronger down
there. Except for afternoon showers, weather should show
significant improvement over the weekend with the possibility of a
quick passing set of showers coming in (deepening upon which model
you look at) late Sunday/early Monday and then after Wednesday.
So far, the 4th of July looks ok (subject to change).


.Eastern Micronesia...
Fair weather is over Chuuk, Pohnpei and
Kosrae today, but surging trade winds and upper-level divergence
are producing heavy showers over the central Marshall Islands.
Patchy showers could hopefully move across the far northern
Marshall Islands in the coming days. GFS Model indicates the
showery weather will spread slowly westward. Kosrae should be just
south of the heavier rainfall, and the surface and upper-level
features may not be as well correlated as the pattern moves
farther west. At any rate, some showers should move toward Kosrae,
Pohnpei and Chuuk by this weekend thru early next week. Although
models indicate briefly improving weather over far Eastern
Micronesia this weekend, relatively wet trade-wind weather may
continue through the longer term. Majuro/Kalo Buoy shows combined
seas of 4 to 5 feet.


.Western Micronesia...
Southwest surface winds are developing across Palau and latest
ASCAT Analysis shows a weak circulation near Koror at 7.5N136.5E.
Also, a surface trough extends northeast from the circulation to
the Mariana Islands, and an upper-level trough is from northwest
of Koror to the far northern CNMI. Satellite shows patchy showers
and thunderstorms developing over Palau and Yap State today. The
circulation is moving northwest and should lift the trough and
showers farther northwest as well, but models indicate a
relatively wet pattern will persist over far Western Micronesia
the next day or two. Improving weather is expected this weekend,
but unstable conditions may develop again next week as showery
weather gradually moves westward from Eastern Micronesia.


Marianas Waters...None.


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