Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
FXPQ60 PGUM 242131

Area Forecast Discussion
National Weather Service Tiyan GU
624 AM ChST Thu Aug 25 2016

PGUA Doppler weather radar shows almost no showers within the
Marianas waters this morning. The VAD wind profile reveals south
winds of 7 to 12 knots through the lowest 4 thousand feet of the
air. The weather balloon from last night shows much stronger winds
which have been weakening, with ASCAT showing 10 knot winds and a
surface ridge approaching.


Little change in forecast philosophy, just an update in taking
something we have been discussing and actually placing it into the
forecast package. Lighter winds and more sun will allow for the
possibility of island convection. The Non-hydrostatic mesoscale
model shows that it expects this to happen today and Friday at
least, so went ahead and added a mostly cloudy spot over Guam each
afternoon along with a few hours of scattered showers and a slight
chance of thunderstorms. By Sunday, the winds pick up a little,
however Saturday will still bear watching. Otherwise, weather will
be laid back with a moderate risk of rip currents through
Saturday. After this it looks like we start to pick up some
northwest swell from Typhoon Lionrock, which could be sufficient
to require a high surf advisory.


.Eastern Micronesia...
Gentle to moderate trade winds are expected from Chuuk State
eastward to the Marshall Islands thru this weekend. A trade-wind
disturbance can be seen between Chuuk and Pohnpei this morning.
Despite the presence of this system, dry subsiding air above 550mb
should maintain partly cloudy skies near Chuuk and Pohnpei thru
Friday, and Kosrae until late this evening. Farther east, another
trade-wind disturbance near 174E is approaching the Marshall
Islands. At the upper levels, a trough is also in the vicinity over
the Marshalls near 170E. Moist divergent flow associated with the
upper trough has been enhancing sporadic convection near the trade-
wind disturbance near Majuro this morning. This trend will continue
for the capital thru tonight. As both features progress farther
westward over the next few days, it will bring similar weather to
Kosrae by early Friday morning, Pohnpei and Chuuk by early Saturday

Latest ASCAT satellite imagery reveals a third trade-wind
disturbance upstream east of the Date Line near 170W. This system
will prolong a relatively wet pattern for all the above locations
thru this weekend. For the first half of next week, general model
consensus is developing a tropical disturbance currently northwest of
Minami Tori Shima and moving it east-northeastward. Under this
scenario, it might introduce a broad surface ridge over Chuuk and
Pohnpei, gentle trades near Kosrae and Majuro. If so, drier weather
is possible toward midweek next week.


.Western Micronesia...
Reasoning for the Chuuk forecast is included under Eastern
Micronesia above.

The monsoon trough connecting Typhoon Lionrock southeast of Okinawa
and a tropical disturbance northwest of Minami Tori Shima has lifted
farther north to near 25N. In response, moderate southwest monsoon
winds have also shifted north of the Republic of Palau and Western
Yap State. This allows a surface ridge south of Guam near 7N145E to
build westward over both places. This feature is going to maintain
fair conditions for the area over the next several days. The only
exception will be the possibility of afternoon thunderstorms near
Koror due to island heating.

Typhoon Lionrock is anticipated to remain in the general area
southeast and east of Okinawa over the next few days. This will
generate a northwest swell toward Palau and Western Yap State. As a
result, expect seas and surf to gradually rise starting Friday. At
this point, Lionrock should not stay long enough to produce swell
high enough to cause hazardous seas and surf for Palau and Western
Yap State.


Marianas Waters...None.


Stanko/Chan is the U.S. government's official web portal to all federal, state and local government web resources and services.