Area Forecast Discussion
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FXPQ60 PGUM 230841
AFDPQ

Area Forecast Discussion
National Weather Service Tiyan GU
640 PM ChST Sun Jul 23 2017

.Marianas Synopsis...
Satellite and radar show mostly cloudy skies with isolated showers
and thunderstorms across the Marianas, mainly over Guam and Rota
waters. Combined seas are generally 2 to 4 feet, with gentle
southeast winds.

&&

.Discussion...
Forecast is little changed, with isolated thunderstorms persisting
through Monday night, followed by drier weather with only isolated
showers the rest of the week. Winds will be slowly shifting around
to the south Monday and southwest by Thursday as monsoon
southwesterlies flow into Tropical Storm/Typhoon Noru wandering
around north of the region. While a persistent monsoon rain band may
bring several inches of rain to the far northern Marianas over the
next 7-10 days, only about an inch is forecast for Guam up to Saipan.


&&

.Marine...
Have reworked the wave and swell grids to reflect the collapse of the
trade winds and associated swell in favor of a developing northeast
to north swell from Noru up north, and a secondary swell from the
southwest generated by the monsoon. Neither swell is expected to be
much more than 3 or 4 feet the next few days, but, depending on how
Noru develops and moves, the north swell could eventually be large
enough to produce high surf along north facing reefs at the end of
this week or early next week, especially for Tinian and Saipan.


&&

.Eastern Micronesia and Chuuk...
Slightly drier air at mid levels should provide fairer conditions
near Chuuk and Pohnpei thru Monday, and at Kosrae until early Monday
morning. A robust trade-wind disturbance is going to bring some
needed rainfall for the Marshall Islands, especially the northern
islands from tonight thru Monday evening. As this disturbance
continues to progress westward over the next few days, showery
conditions will also reach Kosrae by Monday morning, Pohnpei and
Chuuk on Monday night. Decreasing trade winds near midweek should
allow conditions to improve from east to west across the region.
Nevertheless, the remnants of another trade disturbance currently
upstream east of the Date Line near 163W can still bring more wet
weather to the region toward the weekend.

Despite the on-going astronomical high tide or King Tide cycle across
the Marshall Islands for the next few days, there is only a moderate
east-southeast swell of 4 to 6 feet present. This will create a 6 to
8-foot surf on top of high tides, about 1.5 to 2 feet higher than
average. Some splashing waves can occur along coastal roads and near
the airport but significant inundation is not expected.

&&

.Western Micronesia for Yap and Koror...
With the ASCAT satellite data not available, used ship observations
and VIS satellite loops to estimate the latest status on the monsoon
surge across far western Micronesia. The monsoonal circulation,
Invest 99W is quasi-stationary northwest of Koror near 10N130E.
Squall lines embedded within surging monsoonal southwest winds are
visible from Koror southeastward to EQ140E. Ship observations suggest
20 to 30 knot winds south of 3N and 10 to 20 knot winds from 3N to
7N. Therefore waves of squall lines will continue to impact Koror
thru tonight. For Yap, a surface trough moving northwestward north
of the monsoon trough will trigger some thunderstorms by late this
evening. As 99W gradually drifts northwestward Monday and Monday
night, it will reinforce fresh monsoon winds over Koror and spread
them over Yap. Expect inclement weather for both places to last thru
at least Tuesday morning. Once 99W has pulled farther northward into
the Philippine Sea, its influence over the area should gradually
diminish starting Tuesday afternoon. After midweek, a surface ridge
will form and introduce quieter weather.

Building southwest swell created by the surging monsoon winds is
going to cause hazardous surf across the Republic of Palau and
western Yap State thru Tuesday evening. Conditions will also become
hazardous for small craft near Koror by Monday morning and Yap by
late Monday evening.

&&

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

&&

$$

Middlebrooke/Chan



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