Area Forecast Discussion
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FXPQ60 PGUM 230834

Area Forecast Discussion
National Weather Service Tiyan GU
635 PM ChST Tue Jan 23 2018

.Marianas Synopsis...
East trade winds and a few showers prevail across the Marianas this


Little change made to the forecast. Did update the winds with new
model data. Also Cancelled the Fire Weather Watch.

A dry-season weather pattern will prevail across the Marianas through
the coming week. Models show what appears to be a weak shear line
remnant passing over the area Wednesday. This will bring a few clouds
to the local area, but deep-layer moisture is lacking so showers will
remain isolated at best. Earlier forecast had mostly cloudy skies
both Wednesday and Wednesday night, however the latest model data
curtails the moisture and expect these conditions only on Wednesday.
Dry weather will prevail the second half of the week with only
isolated showers at best from Wednesday night through Friday. Models
show a shear line pushing down across the Marianas this coming
weekend with skies becoming mostly cloudy at that time. Skies may
become mostly cloudy ahead of the shear line Friday night. GFS hints
at a brief period of scattered showers Sunday and Sunday night, but
this has not been added to the forecast as confidence in this is low.

Winds will basically remain at 10 to 20 mph through much of the week
with the exception being 10 to 15 mph tonight. Strong high pressure
building off of Asia this coming weekend will help push the shear
line over the Marianas that was mentioned above. The pressure
gradient between the center of high pressure to the north and lower
pressure to the south may produce breezy condition Sunday and Monday.


Tanapag, Ritidian and Ipan buoys show sea heights around 6 to 8 feet.
The rip current risk will remain high on east facing reefs through
Wednesday afternoon. Models decrease the east swell Thursday and the
rip risk on east facing reefs will become moderate.

Ritidian and Tanapag buoys both show a north and east swell. The
north swell will persist through the forecast. Ipan had an east swell.


.Fire Weather...
Wind speeds are predicted to be between 10 and 20 mph though
Saturday. This is below Red Flag Warning criteria and so canceled the
Fire Weather Watch. With winds expected to increase this weekend, a
new Fire Weather Watch may be needed, although relative humidity may
be too high at that time.


.Eastern Micronesia and Chuuk...
Moderate to fresh trade winds are expected from Chuuk State eastward
to the Marshall Islands for the next several days. Divergent upper-
level winds will also persist over Chuuk, Pohnpei and Kosrae thru
Saturday and increase the chance of thunderstorms. A trade-wind
disturbance embedded within these trades will continue to trigger
showery weather near Kosrae thru Wednesday evening, and introduce it
to Pohnpei by Wednesday afternoon and Chuuk on Thursday evening. The
latest ASCAT and VIS satellite imagery reveals a trade-wind
convergence zone between 5N and 10N, stretching eastward from the
disturbance across the Date Line to beyond 160W. This feature will
sustain widely scattered showers near Majuro thru Friday. As it
progresses westward over the next few days, similar conditions will
also spread over Kosrae and Pohnpei thru Saturday, and Chuuk thru
Sunday. By early next week, drier northeasterly trades might finally
usher in fair weather from east to west across the region.

The combination of modest long-period north swell and persistent
trade- wind swell will maintain higher seas across the region thru
the weekend. However, both seas and surf should stay below hazardous
levels; do need to monitor the surf heights on Kosrae though.


.Western Micronesia for Yap and Koror...
A broad surface trough is gradually pulling west of far western
Micronesia this evening. Gentle southerly flow east of the southern
portion of the trough should provide quieter weather near Koror thru
Wednesday. On the other hand, stronger converging southeasterly winds
east of the northern portion of the trough will prolong wetness for
Yap thru Thursday. As the trough moves farther west of the area, the
area of converging winds might trigger a period of showers near Koror
Wednesday night and Thursday. Then a surface ridge building westward
from the east should bring back partly cloudy skies for both
locations toward this weekend. Things could become unstable again
later this weekend as an old shear line drapes across the area.

Fresh winds associated with a potential shear line over the
Philippine Sea will arrive at far western Micronesia this weekend. As
seas and surf start to build by Saturday, need to monitor for small
craft advisory conditions and hazardous surf.


GU...High Rip Current Risk through Wednesday afternoon for GUZ001>004.

     Fire Weather Watch until 6 PM CHST this evening for GUZ001.

Marianas Waters...None.


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