Area Forecast Discussion
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FXPQ60 PGUM 260805

Area Forecast Discussion
National Weather Service Tiyan GU
605 PM ChST Sat May 26 2018

.Marianas Synopsis...
Isolated showers and east winds prevail across the Marianas this


Little change made to the forecast. A relatively dry weather pattern
will persist through much of the forecast. Models show east trade
winds persisting through the weekend and much of the coming week.
Deep layer moisture will not be too high so expect only patchy clouds
and isolated showers.

Models are indicating a circulation near the Marianas by next Friday,
but are not in very good agreement on timing and location of the
weather feature. GFS has a circulation passing south of Guam Friday
and to the west by next Sunday. NAVGEM has a circulation to the east
of the Marianas next Friday. ECMWF has just a large trough over the
area with a circulation forming far to the west of the Marianas by
next Sunday. CMC model has a circulation passing near Guam next
Saturday night and Sunday. While it is hard to say what type of
weather feature will develop, the models probably are hinting at a
wetter weather pattern next weekend. Too early to tell the details
of any amount of shower activity at this point. Anticipate at least
an increase in clouds so added mostly cloudy to the forecast for next


Observations from Ipan, Ritidian, and Tanapag buoys this afternoon
show sea heights of 3 to 4 feet. All three buoys showed an east to
northeast swell. Ritidian and Tanapag also show a north swell and the
models keep this swell through the night. The east swell will remain
high enough to generate a moderate rip current risk there. Models do
show sea heights and the east swell increasing the second half of next
week. This increase will only be slight and the rip current risk will
remain moderate on east facing reefs.


.Eastern Micronesia and Chuuk...
A few weak trade-wind disturbances will continue to move across the
region over the next couple of days. Farther north, an upper-level
trough will persist near 20N thru most of next week. Modest divergent
flow south of this upper trough is going to maintain patchy showers
and a few thunderstorms near the trade disturbances across the entire
region thru Sunday night. Farther east, a trade-wind convergence zone
is visible between 4N and 11N stretching eastward from the Date Line
to beyond 160W. This feature is going to enter the Marshall Islands
Sunday night, Kosrae and Pohnpei on Monday and Chuuk near Tuesday.
Meanwhile, model guidance is suggesting the upper-level trough near
20N to intensify toward middle of next week. If so, increasing
divergent flow south of this trough will likely trigger widespread
deep convection near the trade convergence zone as it makes its way
across the region. As a result, there is the potential for significant
rainfall next week.

Larger trade-wind swell and wind waves are expected to keep surf and
seas elevated from Chuuk State eastward to the Marshall Islands thru
midweek next week. Therefore, rip current risks along east facing
shores will remain higher. Surf heights on Kosrae has been staying
below hazardous criteria so far, will continue to monitor this
situation there.


.Western Micronesia for Yap and Koror...
A slow-moving broad surface trough will continue to couple with an
upper-level trough extending southwestward across the Philippine Sea
to create sporadic convection near Koror thru Sunday. For Yap, drier
air at mid levels should hinder convection there until early Sunday
morning. After the passage of the surface trough, surface ridging
will provide more stable weather for Koror near Monday and Yap on
Tuesday. By midweek, model outputs are forming a near-equatorial
trough across far Western Micronesia. Under this scenario, unstable
conditions will return to the area thru the second half of next week.


Marianas Waters...None.


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