Area Forecast Discussion
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FXPQ60 PGUM 270720

Area Forecast Discussion
National Weather Service Tiyan GU
520 PM ChST Tue Jun 27 2017

.Marianas Synopsis...
An upper-level low near 18N153E is approaching the Marianas. Until
it comes near enough isolated trade-wind showers will predominate.
The buoys reveal combined seas of 3 to 5 feet within the Marianas


Upper-level low will be the main weather feature for the last half
of this week and into the early part of next week. This low will
add isolated thunderstorms to the usual mix, and some periods of
scattered showers could ensue also. The morphology of this low is
a bit unusual in that it is rather large and seems to have 2 sub
vortices within it. This adds to the complexity and is the primary
reason it is difficult to time the scattered showers. Did bring
the thunderstorms in a little earlier than the previous forecast
package based on an extrapolation of recent satellite image and
lightning data. Otherwise little change in philosophy.


.Tropical systems...
The disturbance which came through the Marianas earlier this week
is now near 20N137E. It continues to have an unfavorable upper-
level environment, so models agree on little or no development. It
is expected to track northwestward for a few days then be absorbed
into the Mei-yu front.


.Eastern Micronesia...
A broad and weak circulation south-southwest of Chuuk will
maintain showers and thunderstorms overnight across much of Chuuk
State. Showers with this disturbance extend eastward to near
Pohnpei, where isolated showers and thunderstorms will linger
through tonight. Drier weather eastward at Kosrae and Majuro will
gradually build westward to Pohnpei and Chuuk on Thursday and
Friday. Another disturbance will bring more showers to Majuro by
early Wednesday. Models show this disturbance may weaken as it
progresses westward, with a relatively drier pattern for Chuuk,
Pohnpei and Kosrae in the long term.


.Western Micronesia...
Discussion for the Chuuk forecast can be found under Eastern
Micronesia above.

Generally fair weather will persist at Yap and Koror through
tonight with light and variable winds. A surface trough passes
over or just north of Koror and curves ESE to a weak circulation
SSW of Chuuk. Converging west winds south of the trough are
generating showers and thunderstorms just south of Koror this
evening. The weak circulation/broad area of disturbed weather will
slowly shift WNW bringing unsettled weather to Koror and Yap on
Wednesday and Thursday. Showers remain isolated for now, but will
have to watch closely for scattered coverage. Expect light and
variable winds and drier weather for the weekend after this
disturbance passes by.


Marianas Waters...None.


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