Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
FXPQ60 PGUM 161121 AAA

Area Forecast Discussion...Updated
National Weather Service Tiyan GU
920 PM ChST Sat Dec 16 2017

Update... Showers have decreased to isolated over Guam and Guam
waters as the band of convergence responsible for the convection has
drifted out of the area. The risk of thunderstorms has also

Prev discussion... /issued 525 PM CHST Sat Dec 16 2017/

Marianas Synopsis...
Latest visible satellite imagery shows mostly cloudy skies over
the Marianas this afternoon. Scattered showers and a few
thunderstorms are seen over Guam and Guam waters with isolated
showers over Rota, Tinian and Saipan. latest buoy readings show seas
between 6 and 7 feet.

A monsoon trough stretches southeastward from TS Kai-Tak to a
developing tropical disturbance, Invest 97W, centered well to the
south of Guam. Converging winds north of the trough brought scattered
showers and a few thunderstorms to Guam and Guam waters early this
afternoon. Decided to go ahead and add isolated thunderstorms to the
remainder of the Marianas due to marginal instability across the
area. Otherwise, no changes beyond tonight. Models continue to
struggle with the outcome of Invest 97W. Latest model guidance now
shows this system weakening and a new one developing farther south
and east. The ECMWF develops this new system south of Chuuk, while
the GFS has it further east, developing south of Pohnpei. This
situation will need to be monitored very closely over the next couple
of days.

Moderate winds and seas between 6 and 7 feet continue across the
waters this afternoon. Winds will slowly increase over the next few
days, becoming moderate to fresh Sunday and fresh to strong Monday.
Seas will also build to as high as 10 feet by Tuesday. A Small Craft
Advisory may be needed by Monday afternoon.

Tropical systems...
Invest 97W, now well south of Guam, remains the focus over Micronesia
this afternoon. There is a lot of uncertainty with this system.
Latest model guidance indicates this system will slowly dissipate and
another will form farther south and east. Due to the uncertainty,
this situation will be monitored closely over the next few days.
Regardless, a fairly wet pattern is likely over western Micronesia
and, depending on how the disturbances develop, could push northward
into the Marianas.

Eastern Micronesia...
A surface trough that caused showers over Pohnpei earlier is moving
westward into Chuuk State this evening. Otherwise, surging trade
winds and convergence are triggering spotty showers over Pohnpei and
Kosrae States and the Marshall Islands. By Sunday evening, a much
drier fresh to strong trade surge will usher in pleasant but windy
conditions across the region from east to west. Weather near Chuuk
might be unstable next week, depending on the future developments of
the tropical disturbance to their southwest. If it takes a northwest
track, it could prolong convergent trades over the island. On the
other hand, a west-northwest track would allow drier trades to
arrive from the east.

Moderate trade-wind swell and wind waves will keep marginally
hazardous surf on Kosrae thru Sunday afternoon. By late tonight,
trade-wind swell and wind waves will start to build higher across
the entire region. This will spread hazardous surf into the Marshall
Islands on Monday and to Pohnpei and Chuuk on Monday or Tuesday.
Seas from Chuuk State eastward to the Marshalls will also approach
Small Craft Advisory levels by Sunday and Monday. Finally, a new
King Tide cycle will start on Sunday. Therefore, need to monitor for
possible inundation on Kosrae and Majuro.

Western Micronesia...
The Special Weather Statement was re-issued and High Surf Advisory
remains for Koror. TS Kai-Tak is moving away northwest, while the
monsoon trough runs southeastward over Yap through the disturbance
southwest of Chuuk near 3.5N148E; Invest Area 97W. The pattern is
complicated and there may be several small circulations in the
monsoon trough, and the weather moving across Yap this afternoon
seems to be associated with a mid-level circulation. Models differ
widely on development and movement of 97W. GFS and WW3 Wave Model
still seem too aggressive. Current forecast follows continuity with
previous forecasts with a few small upward adjustments. The main
circulation thats associated with Invest 97W is expected to move
slowly toward west-northwest and gradually develop further over the
next few days, and the situation will need to be monitored very

Winds and waves will likely build across the area over the next few
days with good potential for marine conditions to become hazardous
for small craft operation by Sunday night or Monday through much of
next week.


Marianas Waters...None.


Kleeschulte/Simpson is the U.S. government's official web portal to all federal, state and local government web resources and services.