Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 182134
Area Forecast Discussion
National Weather Service Tiyan GU
734 AM ChST Thu Jan 19 2017
Andersen Air Force Base Doppler weather radar shows scattered
showers in the Guam and Rota coastal waters with isolated showers
in the Tinian and Saipan coastal waters. The VAD wind profile
reveals east-northeast winds of 15 to 20 knots just off the
surface which then increase to between 20 and 30 knots through the
lowest 9 thousand feet of the air.
Shear line is beginning to get thinner and weaken a little. It
will, however, continue to be the big player in our weather
through at least tonight. Winds will only gradually diminish along
with waves. The heavier showers have ended in the Guam and Rota
waters, however coverage is still at scattered levels (at least).
For a few days after the shear line is gone from the Marianas
coastal waters, we will be in a fairly standard dry season trade-
wind regime. During the first half of next week, both the ECMWF-
HiRes and the GFS bring a new shear line in. The timing is a bit
different however. So while the forecast describes a shear line
passage, we are not going full bore yet because of the uncertainty
Buoys continue to read 10 to 12 feet. However, the peak readings
have diminished a little, from 18 to 20 now they are 16 to 18. So,
there is a good chance we are still are on track for early Friday
morning to go back below advisory criteria for small craft. Surf
is also diminishing, went with just marginal hazardous surf today
which is expected to fall below hazardous levels Friday.
Satellite shows showers and thunderstorms in patchy areas along a
near-equatorial trough that runs from southern Chuuk State across
southern Pohnpei and Kosrae States to near Tarawa. Relatively dry,
fresh to strong trade winds prevail at Chuuk, Pohnpei, Kosrae, and
Majuro for the near term. For the longer range, models indicate a
bit more moisture across the region as convergence increases and
patchy showers will return to the area by early next week.
Far northern Marshall Islands remain very dry. Both ECMWF and GFS
show only about a half inch of rainfall north of 10N through the
next 10 days.
Large north swell at Chuuk, Pohnpei and Kosrae will gradually
subside later today and Friday. A building east-northeast trade wind
swell will maintain hazardous surf along Kosrae`s east facing reefs
through the weekend. The combination of long period north swell, the
building trade wind swell and fresh to strong winds over the next
couple days will produce conditions hazardous for small craft at
Chuuk, Pohnpei and Kosrae. The Majuro/Kalo buoy shows combined seas
4 to 5 feet.
Chuuk discussion included with Eastern Micronesia above.
Satellite and ASCAT Winds show a shear line/frontal boundary about
125 miles northwest of Yap this morning, and a surface trough south
of Koror that is moving slowly westward. Trade-wind convergence and
patchy showers over eastern Yap State are also moving westward.
Models indicate more showers arriving at Yap and Koror Today and
Friday as moisture increases between the boundary northwest of Yap
and the surface trough south of Koror. Relatively drier weather
expected at both locations by Monday.
High Surf Advisories remain in effect for Koror and Yap. Large north
swells will cause hazardous surf the next day or two before starting
to subside on Friday or Saturday.
GU...High Surf Advisory until 6 AM CHST Friday for GUZ001>004.
Marianas Waters...Small Craft Advisory until 6 AM CHST Friday for