Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 282124
Area Forecast Discussion
National Weather Service Tiyan GU
724 AM CHST SUN MAY 29 2016
PGUA Doppler weather radar shows only a few showers moving through
the Marianas waters. The VAD wind profile reveals Southeast winds
of 4 to 9 knots through the lowest 6 thousand feet of the
atmosphere. The weather balloon from last night shows this to be
part of a pattern of variable winds 10 knots or less through about
30 thousand feet. Above this winds are Northwest at 10 to 20
Light winds continue through the lowest 30 thousand feet. Visible
satellite imagery shows a relative lack of clouds this morning,
which will allow for daytime heating. Since island convection did
occur yesterday and now we have more moisture in the air due to
the convection yesterday, it is difficult to see how it could fail
today. Previous forecast package mentioned it, so no major changes
were needed. Only thing going against it is less CAPE, probably
due to the vertical heat transfer that occurred during the event
yesterday. A CAPE of 1431 should still be sufficient for at least
today though. Later, the ridge to our north continues to sag
southward. This will likely strengthen the inversion and introduce
some sinking motion, so the island convection will become much
less vigorous and may stop completely. One last note is that the
GFS20 had some rain near Guam yesterday afternoon, so it is
possible that it was actually modeling the island convection.
Until now, only the HiResW-NMM was capable of that, will have to
try to monitor future events. Seas will remain at 2 to 3 feet and
winds 10 knots or less all week. Wetting rain caused by the island
convection will likely mitigate fire danger for a few days at
least. It remains to be seen if more will follow it today, that
would reduce the danger even more.
A weak trade-wind disturbance is departing Chuuk will keep a few
showers there this morning. By later this afternoon, fair weather
already over Pohnpei and Kosrae should also spread westward over
Chuuk. For Majuro, another trade disturbance is triggering showers
and thunderstorms there and this trend will continue thru tonight.
This same disturbance will also bring a period of showers to
Kosrae by late tonight, Pohnpei and Chuuk on Monday and Tuesday.
Farther east, a trade-wind convergence zone can be seen between 4N
and 10N extending eastward from 175E thru the date line to 170W.
This feature is expected to enter the region Monday and prolong
showery weather near Majuro thru at least Tuesday, and might do
the same to Kosrae, Pohnpei and Chuuk later this week.
Reasoning for the Chuuk forecast is included in the Eastern
Micronesia section above.
The southwestern end of a surface ridge lies just north of Koror
and Yap over the Philippine Sea. This feature should maintain
relatively fair conditions for both places thru Monday night.
However, this can also cause afternoon thunderstorms to form near
Koror today and Monday. Near midweek, a weak trade-wind
disturbance currently pulling west of Weno in Chuuk State will
arrive and might increase the chance of showers.