Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 272044
Area Forecast Discussion
National Weather Service Tiyan GU
502 AM ChST Thu Jul 28 2016
Satellite and radar show scattered showers and a few brief
thunderstorms in the Marianas waters. These showers are expected
to decrease in coverage with the approach of sunrise, and become
isolated during the morning. East winds are gentle, and the buoys
are indicating seas around 3 feet.
Considered forecasting scattered showers for early this morning,
but diurnal effects should result in decreasing coverage by
sunrise resulting in isolated soon after. The rest of the forecast
is unchanged with isolated thunderstorms associated with weak
troughs still expected through tonight and again over the weekend.
Light winds may enhance the chances for daytime thunderstorms over
Guam the next few days.
A broad surface trough is going to maintain a few showers and
thunderstorms near Chuuk until Friday evening and Pohnpei thru
tonight. For Kosrae, surface ridging should provide fair weather
thru this evening. This same fair weather pattern should also reach
Pohnpei and Chuuk on Friday. Farther east, a trade-wind convergent
boundary is found between 4N and 8N, stretching east-northeastward
from near Majuro at 170E thru the date line to beyond 160W.
Meanwhile, an upper-level low is centered north of Majuro near
13N170E. Divergent flow south of this low has been enhancing
periodic convection near the convergent boundary. Expect this
convection to persist near Majuro thru Friday.
Over the next few days, the upper low will dig southwestward toward
Majuro and Kosrae which will cause an upper trough near 10N to sink
southward over Chuuk and Pohnpei. As the trade convergent boundary
gradually shifts westward, these upper and surface features will
join forces to prolong unstable weather near Majuro thru Sunday and
introduce it to Kosrae on Friday, Pohnpei and Chuuk this weekend.
After the passage of the convergent boundary, weaker southeasterly
trades should allow a relatively drier regime to spread from east
to west starting early next week.
Chuuk forecast discussion is found in the Eastern Micronesia
discussion. Latest ASCAT/RapidSCAT composite streamline analysis
reveals a near-equatorial trough running eastward from near
Mindanao to a weak circulation centered west of Koror at
7N130E, then turning southeastward to end at EQ140E. Converging
south to southeast winds east of the circulation and north of the
trough will continue to spark sporadic showers and thunderstorms
near Koror thru Saturday, and Yap thru Friday. As the circulation
and trough drift farther westward Friday night and Saturday, a
ridge of high pressure currently southeast of Yap near 5N143E
should build westward and dominate the area later this weekend and
early next week.