Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 180918
Area Forecast Discussion
National Weather Service Tiyan GU
637 PM ChST Wed Jan 18 2017
.Synopsis...This afternoon`s satellite and radar imagery show the
entire Marianas chain of islands under low cloud cover from a
frontal system that reaches from the dateline to the Philippines.
Embedded scattered showers and gusty winds are found throughout.
However, showers are primarily light except in patches along the
leading edge such as just south of Guam, and in thunderstorms
farther to the west. This is one of the strongest storms to dig
this far south in several years. Fortunately, there are now signs
in the imagery that the boundary is beginning to erode along the
.Discussion...Forecast remains the same with little change. Most
models indicate a weakening of the system over the Marianas by
early Thursday, however our forecast keeps the cloud cover and
especially the scattered showers over Guam and Rota through
Thursday night, as the models seem to weaken this system systems
a little too quickly. The weekend looks pretty good with the next
big weather producer not coming until early next week, at the
earliest...depending upon which model you use.
.Marine...Buoy data from Guam and Saipan maintain combined seas of
between 9 and 11 feet. Perhaps a little lower than earlier today
when seas were topping 20 feet on the Ritidian buoy, however
Saipan recently reported a 20 footer so this episode is not quite
over. Energy is still from due north with a secondary from the
northeast...so I am hesitant to weaken the swell/surf on the west
facing shores with north swell easily pushing along the west side
with our NE to SW orientation. Models are in agreement to weaken
the seas over the weekend before pushing back up by late Sunday or
Monday with the arrival of new swells from the north.
Visible satellite shows seasonably dry weather at Pohnpei, Kosrae
and Majuro this afternoon. Trade wind showers have pushed southward
with drier air training in from the northeast. A weak trade wind
surge will build in behind the showers tonight and Thursday and
maintain drier weather into the weekend. Long range outlook shows a
bit more moisture across the region as convergence increases over
the islands. Scattered showers and isolated thunderstorms could
return by early next week.
Large north swells at Pohnpei and Kosrae will gradually subside
tonight and Thursday. North facing surf will remain hazardous
through Thursday. A building east-northeast trade wind swell will
maintain hazardous surf through the weekend along Kosrae`s east
facing reefs. The combination of the long period north swell, the
building trade wind swell and fresh to strong winds over the next
couple days will produce conditions hazardous for small craft at
Kosrae and Pohnpei beginning Thursday.
A trade-wind disturbance is generating scattered showers and
isolated thunderstorms near and south of Koror. Drier weather is
present at Yap, which sits between the frontal boundary to the
north and a disturbance to the south. Models show more showers
arriving to Koror on Thursday and Friday as the disturbance heads
WNW. Increased moisture between the boundary north of Yap and the
disturbance to the south-southwest will also bring more showers to
Yap. Relatively drier weather expected at both locations on
Relatively dry trade winds remain over Chuuk, and models indicate
only spotty showers the next few days. A cluster of thunderstorms
this evening will pass just south of Chuuk, providing some mid and
upper level cloudiness. A trade-wind trough could arrive from the
east this weekend with a few more showers.
High Surf Advisories remain in effect for Koror, Yap and Chuuk.
Large north swells will cause hazardous surf the next day or two
before starting to subside on Friday or Saturday. Similar to
Eastern Micronesia, the combination of the long period north swell,
the building trade wind swell and fresh to strong winds over the
next couple days will produce conditions hazardous for small craft
at Chuuk beginning Thursday.
GU...High Surf Advisory until 6 AM CHST Friday for GUZ001>004.
Marianas Waters...Small Craft Advisory until 6 AM CHST Friday for PMZ151>154.