Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 022143
Area Forecast Discussion
National Weather Service Tiyan GU
745 AM ChST Sat Dec 3 2016
.Synopsis... East to northeast trade-winds and isolated showers
prevail across the local area this morning.
Only a few minor changes made to the forecast. Breezy east winds
of 20 to 25 mph will prevail across the Marianas today. High
pressure building out into the Northwest Pacific will allow the
the breezy winds to persist through Monday.
Isolated trade-wind showers are expected through tonight. A weak
surface trough and trade-wind convergence will produce scattered
showers Sunday through Monday. Earlier forecast had scattered
showers through Tuesday, the latest model data show showers
decreasing Monday night. Trimmed scattered showers from Monday
night and Tuesday, but enough moisture will remain to keep skies
mostly cloudy Monday night and Tuesday.
VAD winds at 2kft this morning showed wind speeds in the low 20
knot range from the east. Expect winds between 20 and 25 knots
through Sunday. Winds will decrease slightly Monday to around 20
Buoy data show seas between 8 and 10 feet this morning. Models
show seas slightly higher further east so had seas of 9 to 11 feet
in the forecast. Seas will decrease slightly to 8 to 10 feet
Sunday night with a further decrease Monday night. A Small Craft
Advisory is in effect because of winds and seas. While winds will
decrease below Small Craft criteria Sunday night seas will remain
high enough through Monday afternoon.
An east swell will prevail through the forecast. A north swell
will persist through Monday night. Surf will be hazardous on east
and north facing reefs with surf heights on east facing reefs
between 10 and 12 feet, 9 and 11 feet on north facing reefs. The
hazardous conditions will prevail through Monday before decreasing
Another fresh trade-wind surge is moving southwest toward the
region from near 12N. The leading element of this surge will begin
to trigger widely scattered showers near Pohnpei and Kosrae late
this evening. Farther east, a near-equatorial trough extends
eastward from near Kwajalein at 9N168E across two low-level
circulations east of Majuro at 8N175E and 8N175W to beyond 165W at
9N. Converging winds near these features are already producing wet
weather near Majuro and this trend will continue thru Sunday
night. Surging trades are going to gradually steer the near-
equatorial trough and embedded circulations westward toward Kosrae
on Sunday, and Pohnpei by Sunday evening. Therefore, wetness is
expected to stay across all three locations thru at least Monday.
Toward midweek next week, weakening trades should allow convection
to decrease near the trough and circulations.
Large east-northeast swell generated by strong to near-gale winds
associated with a shear line will spread eastward from Chuuk State
across the rest of Micronesia on Sunday. In response, hazardous surf
already impacting Chuuk State will also affect the other three
forecast points by Sunday evening. Combined with building wind waves
created by the trade surge, sea heights might reach hazardous levels
for small craft operation near Chuuk, Pohnpei and Majuro by Sunday
Latest sounding data from Chuuk continue to show a layer of much
drier air between 650 and 350mb. This dry layer should hinder
shower coverage at widely scattered category near Chuuk, during
the passage of a trade-wind disturbance today and this evening.
Farther west, a surface trough is moving across Yap and Koror this
morning. A similar layer of much drier air above Yap should also
keep showers at widely scattered coverage today. Without a drier
layer over Koror, scattered showers are expected there until early
Sunday morning. Modest divergent southerly winds aloft will
maintain a chance of thunderstorms for both Yap and Koror as well.
Then a period of fair trade weather is possible near Chuuk and Yap
on Sunday. For Koror, a few lingering showers and thunderstorms
are still possible on Sunday. A developing frontal system
currently over China is going to enter the East China Sea and then
track across southern Japan early next week. This feature might
weaken the mid- latitude ridge enough to allow a broad buffer
circulation south of Yap near EQ139E to lift northward. If so,
converging winds from northwest to northeast of this circulation
could bring more showery conditions to all three places for the
first half of next week.
Refer to the second paragraph under the Eastern Micronesia
discussion above for more detail on hazardous surf and seas across
GU...High Surf Advisory until 3 PM CHST Monday for GUZ001>004.
Marianas Waters...Small Craft Advisory until 3 PM CHST Monday for PMZ151>154.