Area Forecast Discussion
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FXPQ60 PGUM 242217

Area Forecast Discussion
National Weather Service Tiyan GU
817 AM ChST Sun Mar 25 2018

.Marianas Synopsis...
Andersen Air Force Base Doppler weather radar shows scattered
showers well south of Guam with isolated showers in the southern
Guam waters and only a few showers at or north of Guam. The VAD
wind profile indicates northeast winds of 10 knots just off the
ground which turn east and increase to between 20 and 27 knots
through the lowest 8 thousand feet of the air. The buoys reveal
combined seas of 7 to 10 feet, mostly comprised of east-northeast
swell and east wind waves.


Maintained high risk of rip currents along east facing reefs and
small craft advisory. Looks breezy today, although most of the
showers are passing south of us. Upped the clouds today as it is
starting out pretty cloudy, showers should remain minimal though
so kept them isolated. Winds should settle down Monday night or
Tuesday, allowing Marianas weather to return to normal.


Combined seas of 7 to 10 feet and wind gusts up to 30 knots have
required a small craft advisory. It is expected to last through
Monday, then the pressure gradient should relax.


.Eastern Micronesia and Chuuk...
The southeastern end of a near-equatorial trough is shifting westward
away from the region. This allows weak ridging to form over Chuuk,
Pohnpei and Kosrae this morning. As a result, a period of slightly
drier conditions is expected for Chuuk thru Monday, Pohnpei thru this
evening and Kosrae until later this afternoon. Farther east, a trade-
wind disturbance is moving across the Marshall Islands. Wet weather
associated with this system will persist near Majuro thru tonight and
reach Kosrae by later this afternoon. As this system pulls farther
westward over the next few days, it will affect Pohnpei by late
tonight and Chuuk by Monday evening. After the passage of this
disturbance, a modest trade- wind convergence zone will maintain a
relatively wet regime across the entire region thru midweek.

The combination of a modest long-period northeast swell along with
large trade-wind swell and wind waves will prolong hazardous surf
across Chuuk, Pohnpei and Kosrae thru Monday night. Conditions
hazardous for small craft will also continue near Chuuk and Pohnpei
thru Monday, Majuro thru tonight.


.Western Micronesia for Yap and Koror...
The monsoon depression is located near 6.5N and 143E this morning.
Deep convection has been flaring up just west and northwest of the
center. Latest ASCAT satellite imagery indicates winds near and south
of the center are still at the 10 to 20-knot range. The strongest
winds of 15 to 25 knots are concentrated north of the center between
7N and 11N. As the depression gradually tracks west-northwestward
today and tonight, the deep convection will spread over Yap by late
this afternoon and Koror by tonight. Rainfall amounts of 3 to 5
inches is probable for both locations by Monday night. The big
uncertainty on the near-term forecast will be how fast the depression
consolidates today and this evening before passing between Koror and
Yap on Monday. If it stays as a depression, Yap will probably
experience the strongest trade winds north of the center while Koror
will stay on the weaker south side of the system. If it intensifies
into a tropical storm by tonight, both locations can experience
strong to near- gale winds thru Monday evening and a Tropical Storm
Watch/Warning will be needed by this afternoon. Once the depression
has pulled northwest of the area on Tuesday, winds and rain should
steadily decrease. The a surface ridge will take shape and provide
quieter weather for far Western Micronesia during midweek.

Building east-northeast swell and wind waves ahead of the monsoon
depression will cause hazardous conditions for small craft near Yap
thru Monday night, and near Koror by this evening. Seas of 8 to 10
feet today will rise and reach 10 to 13 feet by Monday morning. Surf
of 9 to 11 feet along east facing shores today will increase to 11 to
12 feet this evening, then further to 12 to 14 feet and spread to
north and west facing shores on Monday. Both surf and seas should
gradually subside beginning Tuesday as the system moves away from the


GU...High Rip Current Risk through Monday afternoon for GUZ001>004.
     Fire Weather Watch through Tuesday evening for GUZ001.

Marianas Waters...Small Craft Advisory until 6 PM CHST Monday for



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