Area Forecast Discussion
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Area Forecast Discussion
National Weather Service Tiyan GU
620 PM ChST Tue May 23 2017

.Marianas Synopsis...
East trade-winds and and a few showers prevail over the Marianas
this afternoon.

&&

.Discussion...
Only a few small tweaks made to the forecast. Afternoon satellite and
radar imagery showed hardly any showers over the Marianas. Satellite
Water Vapor imagery also shows little deep layer moisture over the
region. The precipitable water index decreased from slightly over
2 inches last night to 1.68 this morning. What this all boils down to
is a low chance of shower activity tonight, so extended the slight
chance of showers through the night.

Models show little change through the week as a dry season weather
pattern is in place over the local area. Expect only isolated showers
to prevail through the week at best. Model rainfall accumulation
from tonight through Tuesday illustrates the dry weather pattern
as less than an inch of rain is expected over the Marianas that
whole time. These models show even less over Guam with a half an
inch of rain total through Tuesday night.

Models suggest that there may be a period of mostly cloudy skies
Saturday night through next Monday as moisture increases slightly.
Despite the increase in moisture showers will remain isolated in
coverage.

&&

.Marine...
Observations this afternoon from Ritidian, Tanapag, and Ipan buoys
indicate combined sea heights around 3 to 5 feet.

An east trade-wind swell of 3 to 5 feet will persist through
Friday night and generate surf of 4 to 6 feet on east facing reefs.
The surf on all other exposures will be 3 feet or less.
Combined seas and the east swell are predicted to increase slightly
on Saturday.

&&

.Eastern Micronesia...
Latest ASCAT and visible satellite imagery reveal a trade-wind
convergence zone between 3N and 8N, stretching eastward from east of
Chuuk at 155E to just east of the Marshall Islands at 175E. At the
upper levels, a trough is seen across Chuuk and just north of
Pohnpei near 9N. Subsidence associated with this upper-level trough
should maintain fair weather near Chuuk thru Wednesday evening.
Despite the presence of the trade convergence zone, this same
subsidence will also keep shower coverage at isolated category near
Pohnpei until Wednesday afternoon. Farther east, convection related
to the convergence zone is going to continue to impact Kosrae thru
Thursday, Majuro until Wednesday.

The upper-level trough is expected to gradually weaken over the next
few days which should cause subsidence to decrease near Chuuk and
Pohnpei. In conjunction with the trade convergence zone slowly
progressing westward, shower coverage and thunderstorm potential
should gradually increase for Pohnpei by Wednesday evening, Chuuk by
Thursday. Remaining in the core of the convergence zone, anticipate
wetness to stay with Kosrae thru Friday. The back edge of the
convergence zone should push west of the Eastern Marshall Islands on
Wednesday. Therefore, much drier trades will usher across Majuro by
Wednesday evening. These same trades should also reach Kosrae and
Pohnpei by this weekend, Chuuk early next week.

Fresh trade winds associated with a trade disturbance embedded
within a convergence zone will create conditions hazardous for small
craft near Majuro tonight. In the wake of this disturbance and
convergence zone, winds should drop below hazardous levels for small
craft on Wednesday.

&&

.Western Micronesia...
Discussion for the Chuuk forecast is included under Eastern
Micronesia.

A surface trough merging against a ridge axis just west of far
Western Micronesia will produce more wet weather for Koror thru
Thursday. A period of less showers will prevail near Yap thru
Wednesday morning, then showery conditions should return by Wednesday
evening as another surface trough arrives from the east. This second
trough will also prolong wetness near Koror thru Friday. During the
weekend, drier trades at low and mid levels are expected to filter
in from the east and provide fair weather for both places.

&&

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

$$

Ziobro/Chan



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