Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 192124
Area Forecast Discussion
National Weather Service Tiyan GU
639 AM ChST Fri Jan 20 2017
The shear line that has brought much showery weather to the area the
past few days has shifted southeast of Guam allowing clouds to break
up over the Marianas. Scatterometry shows 20 to 25 knot winds over
the area with buoys indicating seas of 8 to 11 feet.
The Marianas will see slightly drier conditions the next couple of
days with a steady and persistent northeast breeze. Models show the
diffuse shear line lifting back over the area Sunday, so have
indicated an increase in shower coverage. Models once again show a
new shear line affecting the region around Tuesday or Wednesday,
which will bring another increase in showery and breezy conditions.
Based on the Ritidian buoy showing seas of 10 to 11 feet, felt it
prudent to extend the Small Craft Advisory through Friday night and
the High Surf Advisory through today. WaveWatch 3 model guidance has
been consistently under-forecasting combined sea heights, however,
the trends have been fairly accurate. Models are all showing a
decreasing trend with seas falling 2 to 3 feet the next couple of
days. Seas will rise back up to hazardous levels by Tuesday or
Fresh to strong trade winds are expected to continue from Chuuk State
eastward to the Marshall Islands over the next several days. Latest
IR and ASCAT satellite imagery reveals a series of surface troughs
embedded within these trades from near Majuro eastward to well beyond
the Date Line near 160W. These systems will keep periodic showers
near Majuro into next week and introduce them to Kosrae by later this
afternoon. As they progress farther westward over the next couple of
days, fair weather near Pohnpei and Chuuk will also give way to
showery conditions by early Sunday morning.
Subsiding north swell has allowed surf across Chuuk and Pohnpei
States to drop below advisory levels. However, persistent trade-wind
swell and wind waves should maintain hazardous surf on Kosrae for the
next several days. Fresh winds and choppy seas will also create
hazardous conditions for small craft from Chuuk State eastward to the
Marshall Islands thru at least this weekend.
Discussion for the Chuuk forecast is included in the Eastern
Micronesia section above.
The passage of an upper-level trough along with a surface impulse
will trigger a few showers and possible thunderstorms near Koror and
Yap today. Then a brief period of drier weather is expected for both
locations tonight. A strong ridge of high pressure currently over
central China is going to exit into the East China Sea and pass near
southern Japan over the weekend. This feature will channel strong
northeast winds across the Philippine Sea which might resurrect an
old shear line and nudge it southward toward Yap and Koror. If so,
anticipate wet and gusty conditions for far Western Micronesia this
weekend and the first part of next week.
Residual north-northeast swell should cause hazardous surf to linger
near the Republic of Palau and western Yap State thru tonight. On the
other hand, persistent east-northeast trade-wind swell will introduce
hazardous seas for small craft near Yap thru the weekend which will
likely spread to Koror by Saturday. Stronger winds associated with
the potential shear line this weekend will also lead to rising swell
and wind waves. Therefore need to monitor for another high surf event
early next week.
GU...High Surf Advisory until 6 PM CHST this evening for GUZ001>004.
Marianas Waters...Small Craft Advisory until 6 AM CHST Saturday for PMZ151>154.