Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 212130
Area Forecast Discussion
National Weather Service Tiyan GU
700 AM ChST Sun Jan 22 2017
Radar and satellite show showers and a few thunderstorms near the
Marianas along a shear line that is lifting northward through the
region. Winds have increased, with scatterometry data indicating 20
to 25 knot winds in the area.
Low-end scattered showers are expected through this evening as the
shear line lifts northward. Deep convection has waned since early
this morning, but felt it prudent to keep a slight chance of
thunderstorms for today as water vapor imagery does show some deep
moisture in the area and radar tops has briefly shown some clouds
reaching up to 50 thousand feet. Monday and Tuesday will be slightly
drier, but then another shear line is expected to drop down over the
area around midweek bringing more passing showers. Also, winds will
increase to between 20 and 30 mph as the shear line reaches the area.
Winds have increased in the area and have reached small craft
advisory levels. Buoys show seas starting to climb, but wave models
show seas staying below 10 feet thus have only issued a small craft
advisory for winds. Models show winds subsiding slightly tonight and
Monday, but increase again on Tuesday. Combined seas will also
increase again around Tuesday, both in response of increasing winds,
but also from a building north swell.
Moderate to fresh trade winds are expected from Chuuk State eastward
to the Marshall Islands thru tonight. A trade-wind convergence zone
between 3N and 6N stretches eastward from near Kosrae at 165E to
southeast of Majuro at 175E. This feature is going to bring unstable
weather to Kosrae later this afternoon, Majuro and Pohnpei by tonight
and Chuuk on Monday night. From 175E eastward thru the Date Line to
beyond 160W, the convergence zone has shifted further north to
between 5N and 9N. This portion of the zone should begin to move into
Majuro and Kosrae Monday, Pohnpei and Chuuk toward midweek. In
conjunction with a fresh to strong trade-wind surge, heightening
trade-wind convergence will prolong wet weather across the entire
region thru midweek.
Trade-wind swell will gradually build over the next few days and
prolong hazardous surf on Kosrae most of the week. Rising trade-wind
swell along with increasing trade winds will also maintain hazardous
conditions for small craft from Chuuk State eastward to the Marshall
Islands thru midweek.
Discussion for the Chuuk forecast is included in the Eastern
Micronesia section above.
The remnants of a shear line is going to keep a few showers and
possible thunderstorms near Yap and Koror today. By this evening, a
strong ridge of high pressure building eastward from the East China
Sea will usher down much drier northeasterly winds across far
Western Micronesia. This should introduce fair and breezy conditions
to both Koror and Yap thru Tuesday morning. Afterward, a trough of
low pressure coming from Eastern Micronesia might cause rainy and
windy weather for the second half of the week.
Increasing northeast winds and swell will maintain hazardous
conditions for small craft operation across the Republic of Palau and
western Yap State thru midweek. It might also create hazardous surf
on both places near Tuesday morning.
Marianas Waters...Small Craft Advisory for winds until 6 PM CHST this evening for