Area Forecast Discussion
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749
FXPQ60 PGUM 032112
AFDPQ

Area Forecast Discussion
National Weather Service Tiyan GU
645 AM ChST Sun Dec 4 2016

.Synopsis...East to northeast trade-winds and isolated showers
prevail across the local area this morning.

&&

.Discussion...
Only a few minor changes made to the forecast. Nixed scattered
showers in today`s forecast. Satellite and radar imagery did show
a few showers over the local area, but not enough coverage to be
considered scattered. Trimmed scattered showers from today`s
forecast. Models do show showers over the local area tonight and
Monday, however 700 mb relative humidity seems to hint that
isolated showers will be the predominant coverage. Considered
taking out scattered showers for tonight and Monday but not too
confident in doing this so left forecast as is tonight and Monday.

Breezy east winds of 15 to 25 mph will prevail across the Marianas
through Monday. Winds will decrease slightly to 15 to 20 Monday night
and Tuesday.

Models show an increased chance of showers Tuesday night through
Wednesday night. Deep layer moisture is not too high so just added
mostly cloudy skies while keeping shower coverage isolated.

&&

.Marine...
Scatterometer data from Saturday night depicted a patch of winds
over the Marianas in the lower 20 knot range, which agrees with
surface observations and the radar VAD winds. Expect winds between
20 and 25 knots through Monday. Buoy data show seas between 8 and 10
feet this morning. Ritidian buoy did record a maximum sea height
of 15 feet, although feel the average will be between 9 and 11
feet today. A Small Craft Advisory is in effect because of winds
and seas. While winds and seas will decrease below Small Craft
criteria by Monday night.

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 on east facing reefs between 10
to 12 feet and 7 TO 9 feet on north facing reefs. The hazardous
conditions will prevail through Monday before decreasing Monday
night.

&&

.Eastern Micronesia...
The leading edge of a fresh to strong trade-wind surge is moving
across Pohnpei and Kosrae this morning and will approach Chuuk
this evening. An upper-level low is also centered north of Kosrae
near 10N166E. Divergent upper-level winds south of this low will
continue to couple with converging trade winds to trigger sporadic
convection over Pohnpei and Kosrae thru tonight. Then slightly
drier trades behind the leading edge might provide less shower
coverage near Pohnpei on Monday. For Chuuk, stronger surface
convergence near the approaching leading edge will be enough to
create periodic showers by late this evening. Farther east, a
near-equatorial trough persists between 4N and 9N, stretching
eastward from the Marshall Islands at 170E across the Date Line to
beyond 170W. Interaction between this feature and the surging
trades has created a series of impulses. The first impulse is
passing over Majuro this morning and will maintain inclement
weather there thru tonight. This same impulse will also sustain
wetness near Kosrae thru Monday, spread to Pohnpei by Monday
evening and Chuuk on Tuesday. More impulses upstream progressing
westward from the near-equatorial trough will sustain wet weather
near Majuro and Kosrae thru Tuesday, Pohnpei and Chuuk thru
Wednesday. After midweek, decreasing trades should allow
convection near these impulses to weaken and fair weather might
return to the entire region from east to west.

The combination of large swell generated by strong winds related to
a shear line and building trade-wind swell will prolong hazardous
surf across Chuuk State and the Marshall Islands thru Monday
afternoon. In conjunction with astronomical high tides, coastal
inundation is also possible at Majuro thru Monday evening. Surf
across Pohnpei and Kosrae States will also rise and reach advisory
levels this afternoon and evening. Aided by increasing wind waves
created by surging trades, winds and seas near Majuro and Pohnpei,
and seas near Kosrae will be hazardous for small craft operation
thru Monday afternoon. Similar conditions might also occur near
Chuuk by Monday afternoon.

&&

.Western Micronesia...
Reasoning for the Chuuk forecast can be found under the Eastern
Micronesia discussion above.

A near-equatorial trough extends southeastward from Mindanao across
3N130E to a broad buffer circulation centered southeast of Yap at
EQ143E. Two trade-wind disturbances can be seen north of the trough
and circulation. One is approaching Koror from 138E and another one
west of Chuuk near 148E. As these disturbances merge with the near-
equatorial trough, this process will generate off and on convection
near Koror thru Monday. Yap being farther north of the trough and
circulation, and with residual drier air loft, mainly isolated
showers are expected thru Monday. With the mid-latitude ridge just
south of Japan continues to weaken over the next few days, the near-
equatorial trough and circulation should begin to lift northward by
Tuesday. Therefore, anticipate convergence induced wet weather to
spread northward over both places and might last thru midweek.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
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.

&&

$$

Ziobro/Chan



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