Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 272032
Area Forecast Discussion
National Weather Service Tiyan GU
632 AM ChST Tue Feb 28 2017
Radar shows only isolated showers in the Marianas waters. Moderate
to fresh trades continue, with 6-8 ft seas at the buoys.
Latest models show no reason to change the forecast from the
previous version. GFS is trimming back rainfall for Thu-Sat with
each new run, by progressively pushing the rain further west. This
brings it into better agreement with the dry ECMWF, and as a result
the forecast of mostly cloudy with isolated showers for that period
still looks good. Overall, the forecast for the next week is a
fairly dry one.
A buffer circulation is centered south of Chuuk near EQ152E. A
surface trough reaches northeastward from it to southwest of
Pohnpei. Converging trade winds north of these features are going
to trigger periodic convection near Chuuk thru Wednesday evening,
Pohnpei and Kosrae thru Wednesday. As these features gradually
pull west-northwestward over the next few days, it should allow
drier trades to return to all three locations by late Wednesday
night. For Majuro, a modest trade-wind convergent boundary between
4N and 8N will spark off a few showers thru tonight. By Wednesday,
a ridge of high pressure passing eastward near Wake Island should
displace this boundary south of Majuro. Farther east of the Date
Line near 6N170W, a trade-wind disturbance and associated convergent
boundary can be seen on the latest ASCAT and IR satellite imagery.
These systems should bring back a showery pattern for the region
from east to west by this weekend.
Declining trade-wind swell and wind waves will remain high enough to
sustain hazardous surf across Chuuk and Pohnpei States until this
evening, and at Kosrae thru Wednesday afternoon. Winds and seas near
Chuuk and Pohnpei will also be hazardous for small craft until this
evening. Despite subsiding seas near Majuro, astronomical high tides
there will remain very high at near 6 feet above mean lower low-water
levels thru this afternoon. Therefore, some minor inundation and
splashing waves are still possible along northeast and east facing
shores until this evening.
A near-equatorial trough persists south of Koror and Yap near 3N this
morning. Drier trades north of this trough should prolong relatively
fair conditions for both places thru this evening. Farther southeast,
a buffer circulation and related surface trough are quasi-stationary
south of Chuuk near EQ152E. As they start drifting west-northwestward
on Wednesday, it will cause the near-equatorial trough to slowly lift
northward closer to Koror and Yap. Aided by divergent southeasterly
flow aloft, isolated thunderstorms are anticipated near both places.
The latest GFS model run seems to track the circulation too far
north, passing north of Yap into the Philippine Sea by Thursday
night. In contrast, both the ECMWF and NAVGEM move it west-
northwestward, taking it between Koror and Yap Thursday and Friday.
No significant development is expected on this circulation as
upper-level wind shear should stay a bit high along its track thru
Thursday. However, it might still produce showery and gusty
conditions for far western Micronesia after midweek.