Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 202128
Area Forecast Discussion
National Weather Service Tiyan GU
457 AM ChST Sat Jan 21 2017
Showers and thunderstorms are flaring up about 100 miles south of
Guam along a shear line. Dry weather is otherwise seen across the
Marianas along with fresh trade winds.
Little change was needed to the forecast as much reasoning remains
much the same. Flaring convection along the shear line to the south
is expected to lift northward toward the Marianas the next 12 to 24
hours. Showers will increase for Sunday then decrease Sunday night
and Monday. Models show another shear line affecting the area around
midweek. Winds will increase early in the week as the new shear line
reaches the area. Stronger winds will be sustained longer as a weak
disturbance passes westward in Micronesia well south of Guam and
strong high pressure passes eastward well north of Saipan.
Buoys show seas of 6 to 8 feet across the Marianas. Seas will drop
around a foot tonight as north swell decreases, but will build to
between 7 and 9 feet Sunday and to between 9 and 11 feet by Tuesday
as another shear line reaches the area, causing winds to increase.
North swell will also build up to between 4 and 6 feet around
Moderate to fresh trade winds are expected from Kosrae State eastward
to the Marshall Islands thru Sunday. Strong trades across Chuuk State
today should decrease to fresh by this evening. A surface trough
embedded within these trades will maintain unstable weather near
Kosrae today. This same area of unstable weather should pass south of
Pohnpei and Chuuk tonight and Sunday.
Farther east, a trade-wind convergence zone between 5N and 9N is seen
stretching eastward from east of the Marshall Islands near 175E thru
the Date Line to beyond 160W. This feature will gradually move
westward across the region over the next few days. Meanwhile, a large
dome of high pressure exiting the East China Coast will begin to
direct stronger trade winds toward the area starting early next week.
Increasing trade-wind convergence might enhance convection along the
convergence zone as it moves over the area. Therefore, anticipate
wetter weather for the entire area starting early next week from east
Residual trade-wind swell will still be big enough to prolong
hazardous surf on Kosrae for the next several days. It will also
maintain seas hazardous for small craft operation from Chuuk State
eastward to the Marshall Islands thru at least Monday.
Discussion for the Chuuk forecast is included in the Eastern
Micronesia section above.
The southwestern end of a shear line is going to trigger showers and
thunderstorms near Yap and Koror thru Sunday. By Sunday evening, the
shear line should begin to weaken which will bring improvement for
both locations. By Monday morning, a strong ridge of high pressure
near the East China Sea will usher down drier northeasterly winds
across the Philippine Sea into far Western Micronesia. Toward midweek
next week, a surface trough currently departing Kosrae might play a
visit to the area.
Declining northeast swell should subside enough to cause surf across
the Republic of Palau and western Yap State to drop below hazardous
levels later today. However, trade-wind swell will be big enough to
sustain hazardous seas for small craft into next week.