Scientific Forecaster Discussion
Area forecast discussion
National Weather Service tiyan GU
540 PM chst sun Oct 23 2016
gentle trades and isolated showers are present across the marianas
this afternoon. Guam buoys show combined seas around 3 to 4 feet.
very quiet weather pattern remains in place across the marianas.
Showers and thunderstorms are seen well to the south near Yap and
Chuuk, none of which will affect the marianas. Vis satellite
imagery shows active weather along 30n and near Japan associated
with a strong frontal boundary. This will come to play in the
marine section below. Regionally, expect quiet conditions to
continue with partly cloudy skies and isolated showers. Will see
gentle trades become moderate by midweek.
combined seas of 3 to 4 feet will persist at least through Monday
night. Wave watch model indicates a long period north swell
building in on Tuesday and Wednesday. Strong winds behind the cold
front just off of Japan will generate the north swell that will
propagate southward. Wave watch model shows a 2 to 3 foot north
swell at Guam and a 4 to 5 foot north swell at Saipan. Marine
grids will need some modification to reflect this north swell.
While this north component will not significantly increase the
combined seas, it could bring up the surf and rip risk along
north-facing reefs Wednesday and Thursday.
a trade-wind disturbance is departing Pohnpei and moving toward
Chuuk this evening. The brunt of wet weather associated with this
system should shift from Pohnpei into Chuuk by Monday morning.
However, residual showers in the wake of this system might linger
near Pohnpei until Tuesday evening. After the disturbance has
passed west of Chuuk near midweek, drier gentle trades will usher
in fair weather for both places.
Farther east, a near-equatorial trough extends east-northeastward
from the southern Marshall Islands at 5n168e thru the date line to
beyond 8n165w. Since Kosrae is situated between the disturbance to
the west and trough to the east, gentle southeast trades should
promote drier conditions there thru Tuesday evening. As the near-
equatorial trough gradually extends westward over the next several
days, modest converging winds near it will maintain periodic
showers near Majuro thru Tuesday night. These showers will
eventually reach Kosrae by midweek. A circulation embedded along
the trough currently at 8n176e might even trigger a few
thunderstorms near both locations toward the weekend.
reasoning for the Chuuk forecast can be found under the eastern
micronesia section above.
An upper-level trough near 10n is digging west-southwestward over
Yap this evening. Subsidence near the trough axis will keep
showers at minimum near Yap thru Tuesday. South of Yap, divergent
flow south of the trough will trigger sporadic convection near a
surface trough. This area of disturbed weather will move over
Koror Monday and Tuesday. Then the upper-level trough is expected
to dig south of Koror and Yap by Tuesday night. This will allow
moderate northeast winds aloft to support a marginal divergent
flow across the area. Along with a trade-wind disturbance
arriving from near Chuuk, clouds and showers are anticipated for
both forecast points thru Wednesday. After the passage of this
second system, a fair trade-wind regime might finally return