Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 261910
Area Forecast Discussion
National Weather Service Tiyan GU
510 AM ChST Mon Feb 27 2017
Moderate to fresh trades and isolated showers are present in the
Marianas. Satellite shows some cloudiness and trade-wind showers out
east of the islands to about 150E. Combined seas are running 5-8 ft
at the buoys.
Once again, the GFS and ECMWF are arguing about what kind of weather
to expect in the Marianas Thursday through Saturday. GFS continues to
be fairly aggressive in developing a broad circulation in the Palau-
Yap region while a shear line drifting down from the NW impinges on
the circulation late in the week. This would result in scattered
showers for the Marianas Thu-Sat. The ECMWF is weaker with the
circulation, and doesn`t bring the shear line as far southeast. This
would result in no more than isolated showers locally. It`s worth
noting, however, that the latest ECMWF just in trends the rain much
closer to Guam Thu and Thu night than previous runs. If this trend
continues, we may indeed be forecasting increased showers later this
week. Stay tuned...
Refreshed the wave and swell grids from Thursday on, as the old grids
were about 2 feet too low compared to latest WW3 guidance and showed
an unrealistic drop in seas over a short time. Otherwise, no other
important changes were made, and seas currently 7-9 feet are now
expected to decrease slowly as the week progresses, to between 5 and
7 feet Wednesday night or Thursday.
Showers and thunderstorms continue to advance northward over Chuuk,
Pohnpei, and Kosrae States. Heavy showers and thunderstorms will
persist at Kosrae through tonight before tapering off on Tuesday. At
Pohnpei and Chuuk, showers will gradually increase tonight and
Tuesday. The band of trade-wind convergence and showers will
eventually push back to the south around midweek, bringing increased
activity to Kosrae on Wednesday. Majuro is still expected to stay
mostly dry with only isolated showers and partly to mostly cloudy
Winds and seas will remain hazardous to small craft the next day or
two from Chuuk to Kosrae. Hazardous surf will persist at the three
locations through at least Tuesday. At Majuro, the risk of inundation
at high tides continues to decrease.
A weak near-equatorial trough southeast of Koror sparked a few
thunderstorms Sunday evening and overnight, but convection has been
quite lackluster overall. Weather at both Yap and Koror will stay
fairly quiet the next couple of days, but a disturbance will bring
increasing showers and thunderstorms Wednesday and Thursday. ECMWF
is coming closer to the GFS with showers spreading farther north.
Both models, along with the Navgem, keep a weak circulation in the
area near or south of Yap. Winds will shift to southeast late in
the week as the system drifts west.