Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 240732
Area Forecast Discussion
National Weather Service Tiyan GU
500 PM ChST Tue Jan 24 2017
Mostly cloudy skies, isolated showers and fresh to strong trade winds
prevail across the Marianas this afternoon.
No changes to the inherited forecast or forecast reasoning. Both the
GFS and ECMWF show a weak system moving westward, south of 10N, over
the next few days. The ECMWF shows the system as an open trough,
while the GFS shows a weak circulation. Either way, both models show
the majority of the shower activity remaining south of the Marianas.
The GFS is more aggressive with the system, though it has been
trending more toward the ECMWF solution over the past few days.
Therefore, made no changes to the forecast, maintaining isolated
showers with mostly cloudy skies through the weekend.
High pressure building over the northwest Pacific will help to
maintain breezy conditions across the islands through at least
Latest buoy observations continue to show seas between 8 and 10 feet
at Tanapag, and between 10 and 12 feet at Ritidian. Latest model
guidance is averaging 1 to 3 feet too low with current observed sea
heights, with seas of 7 to 9 feet predicted through Thursday. Since
seas are expected to maintain current levels through at least
Thursday, before beginning to subside, maintained sea heights between
9 and 12 feet across the Marianas waters, with seas beginning to
subside Thursday night. The seas are comprised of a longer period
north swell and a building northeast swell. The north swell will
maintain hazardous surf conditions for north and west exposures while
the northeast swell keeps border line hazardous surf conditions along
east facing reefs.
Building high pressure over the northwest Pacific will help to
maintain fresh to strong winds across the Marianas through at least
Thursday. Due to these winds combined with seas in excess of 10 feet,
a Small Craft Advisory will remain in effect through Thursday
A trade-wind trough between Pohnpei and Kosrae and a trailing zone
of trade-wind convergence will keep showers and thunderstorms across
the region from Chuuk to Majuro, especially between 4N and 10N.
Models show showers quickly dissipating early Wednesday morning at
Majuro leaving much drier weather in the area for midweek, but more
showers will return by the weekend as another strong trade-wind surge
reaches the area. Similarly, Kosrae will see increased showers late
in the weekend. Showers and thunderstorms will persist at Pohnpei and
Chuuk another day or two before letting up some later in the week.
Hazardous surf is still found across the region from Chuuk eastward,
except for Majuro. Swell and wind waves will subside slightly such
that surf will fall below hazardous levels at Chuuk and Pohnpei by
Thursday. Kosrae will see hazardous surf continuing into the weekend.
Both winds and seas are expected to subside further such that
conditions at Chuuk, Pohnpei and Majuro will no longer be hazardous
to small craft by Wednesday night or Thursday.
The trade-wind surge at Majuro this week will occur in sync with a
full moon. This will lead to increase high tide heights and could
cause some minor inundation along shores facing northeast.
A shear line is found just north of Koror and Yap. Strong winds of 20
to 25 knots are seen across the region from just north of Koror
northward. Showers and thunderstorms are seen just to the southeast
but models keep most activity away from the two locations in the
short term, however, the system will reach the area by Wednesday
night or Thursday. Both Yap and Koror will see increasing showers
and thunderstorms with strong winds persisting through Friday.
Lighter winds and isolated showers are expected over the weekend.
Winds and seas will be hazardous to small craft as hazardous surf
remains in the area due to the strong northeast winds. Seas of 11 to
14 feet will be in the area through Thursday night, then both winds
and seas will slowly subside.
GU...High Surf Advisory until 6 PM CHST Thursday for GUZ001>004.
Marianas Waters...Small Craft Advisory until 6 PM CHST Thursday for