Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 052124
Area Forecast Discussion
National Weather Service Tiyan GU
715 AM ChST Tue Dec 6 2016
.Synopsis... East trade-winds and isolated showers
prevail across the local area this morning. A relatively
dry trade-wind pattern is expected through the week.
Only a few minor changes made to the forecast. Did
update winds through Saturday with newer GFS model data.
Satellite imagery this morning shows a few large patches of
clouds to the east of the Marianas. Models do show patches of
showers over the local area tonight through Thursday. These
showers are probably the result of trade-wind convergence. Deep
layer moisture is not too high so just expect periods of mostly
cloudy skies while keeping shower coverage isolated. Breezy east
winds of 10 to 20 mph will prevail across the Marianas through
GFS, and to a lesser extent ECMWF, have been hinting at a
circulation developing south of 10N late this week and into the
coming weekend. This will have no direct effect on the Marianas
even if it did develop. GFS forms it further north than ECMWF
does. Wind-flow convergence north of the circulation will generate
areas of showers. If GFS is correct, and the circulation does
form, than scattered showers would be possible Sunday through next
Wednesday. If ECMWF is correct than the Marianas would remain dry
as the rain would stay too far south. It is too early to add to
the forecast and because of the uncertainty is not even considered
in the extended forecast.
Radar 2kft VAD wind speeds from this morning averaged in the mid
20 knot range. Expect winds between of 15 to 20 knots through the
day. Models keep the same basic wind speed and direction through
the week, that is east winds of 15 to 20 knots.
Buoy data show seas between 7 to 9 feet this morning. Models show
the seas remaining at this height through Wednesday before decrease
a little Wednesday night.
An east swell will prevail through the forecast. As the swell will
change little the next day or two expect surf on east facing
reefs to be between 8 to 11 feet and 5 to 8 feet on north facing
reefs. Do not expect any small craft conditions through the week.
A surface trough and trade-wind convergence is causing widespread
showers and thunderstorms just south of Chuuk and near Pohnpei and
Kosrae. The bulk of convection will quickly move to the west along
with the surface trough but models indicate a narrow band of
showers and thunderstorms remaining across the area. Although
showers will decrease, there will still be a small chance of
thunderstorms at Chuuk and Pohnpei the next several days and at
Kosrae through Wednesday. Fair weather at Majuro will slowly
spread west later in the week.
Winds are gradually decreasing near Kosrae and Majuro. As a result
have dropped the Small Craft Advisory at both locations. Similarly,
surf has fallen below hazardous levels at Majuro. However, hazardous
surf persists from Kosrae to Chuuk, with winds and seas hazardous to
small craft at Pohnpei and Chuuk.
Reasoning for the Chuuk forecast can be found under the Eastern
Micronesia discussion above.
A near-equatorial trough and disturbance centered near 3N140E will
keep unsettled weather across Yap and Koror. Showers the next
several days will be scattered at times as the disturbance moves
northwestward. GFS and ECMWF show two completely different scenarios
with GFS depicting a tropical cyclone developing. This is in stark
contrast to the ECMWF which shows the near-equatorial trough well
south of Koror. For now, have not made much change in the long-term
forecast. ECMWF has had a better track record on handling these
disturbances versus the, sometimes, more-aggressive GFS.