Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 251952
Area Forecast Discussion
National Weather Service Tiyan GU
545 AM ChST Wed Oct 26 2016
.Synopsis...East to Northeast trade-winds and isolated showers
prevail across the Marianas this morning.
Did update winds with new GFS40 data and added thunderstorms to
today`s forecast. otherwise little change to current forecast.
2kft VAD wind profile indicted winds from the east at around 15
mph. Satellite imagery showed an area of showers just tio the east
of the Marianas. Projecting the motion of these showers brings
them over the local area after 10 a.m. this morning. Could not
find any surface feature that would account for them so they are
probably a manifestation of upper-level winds. Do not expect an
significant increase in coverage with the showers so kept isolated
in the forecast. No lightning was observed with the showers but
because of the convective nature of the showers area added
isolated thunderstorms to the forecast today. Trade-wind
convergence will bring some clouds to the Marianas Thursday night.
A surface trough will form south of Guam this weekend. This will
increase clouds and the chances of showers and thunderstorms over
the Marianas Saturday through Sunday night, Models keep deep layer
moisture low so shower coverage is expected to remain isolated
A weak circulation passing south of Guam will keep skies mostly
cloudy Monday and Tuesday.
Buoy data show seas between 4 to 5 feet this morning. There is an
east swell and Ritidian buoy did show a north swell. Models show both
swells persisting through the forecast. Expect surf on east facing
reefs to be 4 to 6 feet today. Surf on north facing reefs will be
3 to 5 feet but is expected to increase slightly tonight.
A trough remains stretched across the area from near Kosrae to
Kwajalein and farther east-northeast. On a smaller scale, a weak
circulation is found between Kwajalein and Majuro. Heavy showers
and thunderstorms nearby have kept winds gusty and somewhat
variable in direction overnight, but the circulation is expected
to be short- lived and the trough should begin to slowly drift
northward through tonight. This will induce a south to southeast
wind across Kosrae and the Marshalls. Wet conditions will persist
at Majuro and Kosrae to start the day, but showers will lessen
later today while isolated thunderstorms persist in the region due
to the trough nearby. Variable winds at Pohnpei will shift to
south by late week.
Winds overnight have increased seas across the Marshalls but seas
will fall about 1 to 2 feet by weekend as winds subside.
A weak circulation near 3N133E continues to drift west. Showers
and thunderstorms are beginning to redevelop to the east but are
expected to stay mostly south of Koror. Trade-wind convergence
near Chuuk will cause scattered showers this morning, but those
will taper off around midday. Models continue to show a wide
spread in the outlook for the region. While GFS has bounced around
with a monsoon trough forming along 5N or well south of Koror,
ECMWF has been more consistent with a monsoon trough forming along
6N and extending toward Chuuk by late week. Both models show an
unstable pattern conducive for isolated thunderstorms, but neither
suggests any certain time period for increased coverage in showers
at this time. Have modified the winds at Koror to more closely
follow ECMWF guidance in the long term.