Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 232136
Area Forecast Discussion
National Weather Service Tiyan GU
624 AM ChST Tue Jan 24 2017
.Synopsis... Northeast trade-winds and isolated showers prevail across
the local area this morning.
A shear line was draped across the Marianas this morning. The shear
line will remain over the local area through at least Thursday
night. With the shear line over the area mostly cloudy skies will
prevail through Thursday night. Even though skies will be mostly
cloudy, showers will remain isolated as deep layer moisture will
The GFS shows a circulation passing south of the Marianas and south
of 10N Wednesday through Friday while the ECMWF does not. The GFS
hints at low-level convergence north of the circulation prolonging
the mostly cloudy skies over the Marianas through at least Friday
night. GFS also suggest that period of scattered showers are possible
during that time. The ECMWF does not show this and appears more
realistic at this time...so kept showers isolated through the
High pressure building out into the northwest Pacific will keep winds
breezy across the Marianas through at least Thursday.
Buoy data showed combined seas between 8 and 11 feet. This is is the
highest 1/3 average sea height. Ritidian buoy recorded the highest
waves at around 15 feet.
Models keep heights of 7 to 9 feet the next few days...which is below
what is being observed. Kept sea heights above model guidance to
conform to actual observations. An east and a north swell will
prevail through the forecast. Buoy data showed the north swell
around 6 feet, which again is higher than the model. The east
swell will be around 3 to 7 feet. The north swell will produce
hazardous surf on north and west facing reefs of 8 to 10 feet
today increasing to 10 to 12 feet Wednesday. The east swell will
produce hazardous surf of 9 to 12 feet on east through at least
Thursday. Hazardous surf is expected through Thursday.
As mentioned above...high pressure building out into the Northwest
Pacific will keep winds elevated through at least Thursday. Expect
winds over the coastal area between 20 to 25 knots with higher
gust possible through at least Thursday.
With seas around 10 feet and wind between 20 and 25 knots a small
craft advisory will continue through Thursday.
A trade-wind trough and associated convergence are producing
scattered showers and isolated thunderstorms in the southern
Marshall Islands, just north of Kosrae and just south of Pohnpei.
This area should shift to the west and possibly a little north as
time goes on. Therefore, the showers should decline at Majuro
after today due to westward movement and at Kosrae after today due
to northward propagation. The showers will continue at Pohnpei
possibly through Wednesday night as a northward shift and westward
movement will both put them right in the thick of it. Afterward, a
more normal trade-wind regime will set back up.
East swell will maintain hazardous surf at Majuro Today and
possibly Tonight. Due to the lower criteria, the east swell will
maintain high surf at Kosrae possibly through this weekend.
Meanwhile, north swell at Pohnpei will maintain hazardous surf
there today. Surf at Pohnpei is expected to fall below hazardous
levels tonight. However, of some concern is the fact that with
waves forecast to remain somewhat elevated and astronomical tides
increasing, the PacIOOS wave runup forecast for Majuro is reaching
well into the red. We will need to keep an eye on this.
As the shear line continues to retreat to the north, its affect on
Western Micronesia will continue to decline. The current area of
disturbed weather should pass just to the south of Koror, helped
along by fresh to strong northeast flow associated with the shear
line. The area of convergence affecting Eastern Micronesia is just
reaching Chuuk. It will continue to affect Chuuk through Wednesday
at least. As it shifts westward along with the moving trough, it
will reach Yap around Wednesday night and Koror around Thursday.
Similar to Eastern Micronesia, once it passes, a more standard
trade-wind regime will build in.
North swell will maintain hazardous surf on Chuuk today. On Yap
and Koror, where northeast swells are bigger, surf will remain
hazardous through at least Thursday.
GU...High Surf Advisory until 6 PM CHST Thursday for GUZ001>004.
Marianas Waters...Small Craft Advisory until 6 PM CHST Thursday