Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 010753
Area Forecast Discussion
National Weather Service Tiyan GU
550 PM ChST Sat Oct 1 2016
Mostly cloudy skies with isolated showers and gentle to moderate
winds prevail over the Marianas this afternoon. A weak disturbance
is seen on satellite to the north of Chuuk.
No major changes made to the inherited forecasts. Isolated showers
are seen across the Marianas this afternoon. Scattered showers and
isolated thunderstorms are seen to the north of Chuuk associated
with a weak disturbance located in that area. This disturbance
will continue to move toward the Marianas, bringing increased
convection to the waters and islands Sunday. Isolated thunderstorms
are likely by Sunday morning, with scattered showers by afternoon. A
trade-wind pattern is then expected to return to the region by
Tuesday, with drier conditions expected through the following
Gentle trade winds will maintain fair conditions near Pohnpei
thru Sunday and Kosrae until late tonight. To the east, a
pronounced trade-wind convergent zone can be seen between 3N and
6N, stretching east-northeastward from near Majuro at 170E across
the Date Line to beyond 160W. This feature will gradually make its
way westward across the entire region over the next several days.
Expect inclement weather associated with this zone to reach Majuro
by Sunday morning, Kosrae by Sunday afternoon and then Pohnpei on
Sunday night. After midweek next week, decreasing trade-wind
convergence might provide some improvement from east to west.
A surface trough is slowly moving away from Chuuk this evening.
Therefore, shower and thunderstorm coverage near the island
should slowly decrease starting Sunday morning. By Sunday evening,
drier weather already over Pohnpei will also reach Chuuk. Things
might become wet again toward midweek next week as a trade-wind
convergence boundary approaches from the east.
Based on the latest ASCAT satellite imagery, the wind field of
Tropical Storm Chaba over the Philippine Sea near 16N136E has
expanded and acquired more monsoonal characteristics. As a
result, converging southwest winds have once again formed over
Koror and Yap. This has caused sporadic convection to flare up
near Yap this afternoon and will spread westward over Koror by
Sunday morning. Upstream to the east, a surface trough is
departing Chuuk and will begin to interact with monsoonal
southwest winds as it moves toward 145E. All models are hinting
this interaction might spin up another circulation just south of
Guam near Sunday night. If so, it will sustain convergent
southwest winds across Koror and Yap thru at least Monday night.
In coincident with an upper-level trough extending southwestward
from just east of the Mariana Islands, locally heavy downpours are
possible for both places. Once both Chaba and the potential
circulation have moved northwest of the area near midweek next
week, things should begin to quiet down.
Tropical Storm Chaba has slowed down a little today but should
pick up speed later tonight and Sunday. Despite this, ASCAT
imagery indicates the strongest winds are concentrating north and
east of the center. Therefore, weaker winds west of the center
should not generate a northwest swell big enough to cause
hazardous seas and surf across the Republic of Palau and Western
Yap State. However, it is still needed to monitor the wind field
of Chaba over the next few days.