High Surf Advisory 21, NWS Guam

Area Forecast Discussion
National Weather Service Tiyan GU
709 PM ChST Mon Feb 27 2023

.Marianas Synopsis...
Satellite and radar imagery show partly cloud skies with isolated
showers over the waters. Altimetry shows 5 to 6 foot seas near Guam
but 10 to 11 near Alamagan. Ritidian buoy confirms the altimetry near
Guam at 5 to 6 feet.

&&

.Discussion...
Only a few changes made since the previous the last discussion. The
shearline has moved into the region and is crossing near Alamagan, it
is heading southward. Winds are expected to pick up as it moves
south. The POPs (Probability of Precipitation) are expected to
gradually go up from around 10% up to 30 % through the rest of the
week. For the weekend, two troughs appear to be coming in to the
area, one on Friday and one on Sunday. These troughs will keep the
POPs in the 30's for those days.

&&

.Marine...
A fast moving swell is approaching us form the north west and will
be here by Wednesday. Expect seas and beaches to be at the high end
of hazardous and the rip current risk to be high. The shearline is
expected to make winds at sea in the fresh to strong range with
gusts up to the high end of near gale, though some may exceed that.
Tinian and Saipan seem to be getting the brunt of this wind event.
Surf will start to build tomorrow and may get up to 11 feet by
Thursday night. Reefs that will be affected are east, north and west.
Seas are expected to be back to safe levels around Saturday or
Sunday.

&&

.Eastern Micronesia...
Satellite imagery shows a band of clouds near Pohnpei and Kosrae,
and an area of clouds just east of Majuro. The band near Pohnpei and
Kosrae is being generated by weak trade-wind convergence. Only
expect mostly cloudy skies with isolated showers at those two
locations. The clouds near Majuro are being produced by a weak
surface trough. Models show this trough dissipating and only mostly
cloudy skies and isolated showers are expected at this location.

High pressure passing to the north will push drier air into the
area. Expect isolated showers at all three locations the next few
days. Trade-wind convergence will bring scattered showers to Majuro
Wednesday night.

Trade-wind convergence induced showers will spread over the area the
second half of the week. Expect a higher chance for showers at
Pohnpei Friday night through Sunday and Saturday night and Sunday at
Kosrae. A trade-wind disturbance moving through the convergence area
will bring a higher chance of showers to Kosrae Sunday night and
Monday and on Monday at Pohnpei. The trade-wind convergence will also
bring a higher chance of showers to Majuro Wednesday night and again
on Saturday night and Sunday.

High pressure passing to the north will increase the pressure
gradient and increase the winds over portions of the area. This will
produce breezy conditions at Pohnpei Saturday night through Monday
and Sunday through Monday.

&&

.Western Micronesia...
The near-equatorial trough has been pushed down to the equator and
only a few showers could be found near Palau and Yap this afternoon.
Only expect isolated showers at both locations tonight.

A small surface trough will bring a scattered showers to Yap Tuesday
and an increase in clouds to Palau Tuesday night. The near-
equatorial trough will move northward by the end of the week. This
trough and associated low-level convergence will bring a higher
chance for showers to Palau Saturday night through Monday. This
convergence will increase enough to bring a higher chance of showers
to Yap Sunday night and Monday.

Further east...satellite imagery shows an area of showers and
thunderstorms south of Chuuk this afternoon. This area is associated
with a trade-wind disturbance. Models keep this area south of Chuuk
and only isolated showers are expected there tonight. Little will
change the next few days as models show activity remaining south of
Chuuk through Friday night. Expect only isolated showers at Chuuk
through during that time. Low-level convergence north of the near-
equatorial trough will produce a higher chance of showers at Chuuk
Saturday through Monday.

High pressure passing to the north will increase the pressure
gradient over the area. This will cause elevated winds over portions
of the region. Expect breezy conditions at Yap Tuesday, and Tuesday
through Wednesday at Chuuk.

A shear line has pushed down from the north and stretches over the
Philippine Sea. Strong winds behind the shear line will push swells
southward over Palau and Yap. The increased swells may briefly cause
a rise in combined seas to 10 feet at Yap Tuesday night through
Friday night and Wednesday and Wednesday night at Palau. Seas this
high will be hazardous to small craft. Seas may reach advisory levels
but winds are not predicted to. A northerly swell will push into the
area by midweek. It is expected to produce surf up to 7 feet on
north facing reefs of Yap and Palau Wednesday night through Friday.
This is not hazardous, but should be monitored as models may be too
low.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
MP...None.
Marianas Waters...None.
&&

Marianas: Bowsher
Micronesia: Ziobro