Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 290039
Area Forecast Discussion
National Weather Service Tiyan GU
1034 AM ChST Thu Sep 29 2016
Have updated zone and marine forecasts to account for Flood Watch
cancellation, and also to tone down shower forecast today for Guam
.Prev discussion... /issued 711 AM CHST Thu Sep 29 2016/
Andersen Air Force Base Doppler weather radar shows numerous
showers and isolated thunderstorms east of the Guam and Rota
waters. These are associated with Tropical Depression Chaba (21W).
As Chaba moves west these showers will likely be dragged across
Guam and Rota. The VAD wind profile reveals south winds 10 to 20
knots through the lowest 8 thousand feet of the air. By 12
thousand feet they have turned to southeast then east. Above 22
thousand feet they turn back to the southeast.
Ritidian buoy never exceeded 8 feet and is now on a decreasing
trend. Only a few of the highest gusts ever really met the wind
criteria for small craft advisory, and these gusts are abating
now. Went ahead and canceled the small craft and high surf
advisories for that reason. Also canceled the flood watch for
Tinian and Saipan which have been high and dry all night with
little in the way of heavy rain moving in. Retained it for Guam
and Rota for the time being as they received copious antecedent
moisture yesterday with a significant threat of more to come
Weather will improve dramatically Friday, then all eyes turn to
the next disturbance. The position is still up in the air, the
previous run took it just south of Guam and the new one took it
just south of Tinian. Either could allow it to have a significant
impact on weather in the Marianas in the next Monday to next
Tuesday time frame. We already have scattered showers that period
so no changes were needed at this time. Will review further as it
Tropical Depression Chaba (21W) continues to move west. Since it
is now west of the Marianas, it is moving away from us. It should
start to intensify now, however it is already far enough away that
the effects should be rather muted.
Showers and thunderstorms are seen near Pohnpei and Kosrae as a
surface trough nears the area. The trough extends northeastward
across Kwajalein. Majuro will see wet conditions ending this
afternoon and Kosrae will see some drying by tonight. Showers and
thunderstorms will increase at Pohnpei today and persist through
Saturday. The trough will continue west over the weekend, bringing
deteriorating conditions to Chuuk for much of the weekend. Drier
weather will spread from east to west today but another surface
trough will bring increased clouds and showers to the region early
Benign sea conditions are expected at Majuro the next several days.
However, PACIOOS Wave Run-Up Forecast shows higher seas late this
week through weekend with the New Moon phase. Water levels will be
high during high tides through October 3. Inundation is not expected
at this time as combined seas will be between 3 and 5 feet.
Majuro/Kalo Buoy shows combined seas around 3 feet.
Reasoning for the Chuuk forecast is included in the Eastern
Micronesia section above.
Showers and thunderstorms continue at Koror early this morning but
will taper as a low-level ridge spreads over the area. Winds will
shift to the southwest at both Yap and Koror by tonight as Tropical
Depression Chaba moves farther to the west of the Marianas. Weak
monsoonal flow will cause showers and thunderstorms to increase at
both locations the next couple of days. Early next week, models show
the disturbance in eastern Micronesia approaching the area and
bringing more unstable weather to the area.
Moderate long-period northwest swell produced by distant Typhoon
Megi, now over China, will cause higher seas and surf across The
Republic of Palau and Yap State the next couple of days. However,
both seas and surf should remain below hazardous levels.