Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 300717
Area Forecast Discussion
National Weather Service Tiyan GU
511 PM ChST Thu Mar 30 2017
.Marianas Synopsis... East winds, mostly cloudy skies and isolated
showers prevail across the local area this afternoon.
Little change made to the forecast. Updated winds with new GFS
model data. East winds of 10 to 20 mph will prevail across the
Marianas through Friday night as high pressure centered to the
north increases the pressure gradient.
A weak shear line will produce mostly cloudy skies and patchy
showers over the local area through Friday night. GFS model hints
at a surface trough pushing over the Marianas Sunday night and
Monday. Models keep deep-layer moisture shallow through the weekend
and Monday so only expect isolated showers at that time. GFS and
ECMWF depicts a shear line pushing down to near Saipan next Tuesday.
The shear line itself may not make it much further south but
trade-wind convergence near it will increase clouds Tuesday night
through at least Thursday. Showers still are expected to remain
Observations this afternoon from Ipan, Ritidian and Tanapag buoys
indicate combined sea heights of 8 to 11 feet. There is a north
swell of of around 6 feet entering the area. The north swell has a
period of 13 seconds. Calculations predict surf on north facing
reefs of between 8 and 10 feet, which is hazardous. Expect the north
swell to remain this high through the night before decreasing on
Friday. At this time expect the north swell to drop far enough by
Friday night so that hazardous surf is no longer expected.
Winds over the Marine area will be in the 20 to 25 knot range with
occasional gust to 30 knots tonight. Winds this high are a hazard to
small craft. Winds will decrease below criteria, to 15 to 20 knots,
on Friday. While the winds may decrease below small craft criteria
on Friday seas will not. As mentioned above, buoy data indicates
that the combined seas are between 8 to 10 feet. The highest sea
height observed by a few of the buoys shows seas going up to 15
feet at times. Expect seas this high to persist through at least
Scattered to numerous showers and a few thunderstorms are seen
near Pohnpei and Kosrae ahead of a trade-wind surge. Northeast
trades will eventually push showers to the south of Pohnpei early
Thursday morning but showers will persist another couple of days
at Kosrae. Farther east, more clouds and a few showers are seen
south and east of Majuro. This area will expand and move westward
late in the week and into the weekend, keeping Kosrae mostly
cloudy with isolated thunderstorms. Most showers are expected to
stay south of Majuro, although the atoll could see an increase in
showers around Friday.
High surf advisory continues at Kosrae until Thursday evening as
trade-wind swell eventually subside. Also, both Majuro and Kosrae
may still see some inundation around times of high tides through
A disturbance southeast of Koror and Yap is generating widespread
cloudiness and showers in the area. Showers will increase at
Koror tonight and continue through Friday as the disturbance
drifts westward. Yap will see isolated showers and a small chance
of thunderstorms the next couple of days.
Showers at Chuuk will continue on through tonight but gradually move
off to the southwest by Thursday morning as stronger northeast
trades push the convergence boundary farther southwest and drier air
moves into the area.
GU...High Surf Advisory until 6 PM CHST Friday for GUZ001>005.
Marianas Waters...Small Craft Advisory until 6 PM CHST Friday for PMZ151>154.