Area Forecast Discussion
Issued by NWS Tiyan, Guam

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FXPQ50 PGUM 121015 CCA

Area Forecast Discussion...Updated
National Weather Service Tiyan GU
630 PM ChST Thu Dec 12 2019

Updated and corrected to add Micronesia dicussion

.Marianas Synopsis...A pleasant dry-season regime exist around the
Marianas today with a few trade-wind showers visible in the
satellite imagery and easterly winds generally moderate but,
breezy at times. The two buoys sit at between 5 and 6 feet.


.Discussion...Little change in the forecast other than a couple of
tweaks in cloud cover to account for a couple of trade-wind
surges. Timing of each are a bit problematic, but want to indicate
the we will get some cloud cover and showers on a periodic basis
over the next week. Both the ECMWF and GFS show some possible
activity well to the south of the Marianas by late next week, but,
again, I just indicated a slight increase in cloud cover to
account for this. Otherwise, not significant features are


.Marine...Followed the tabular data for the GFS version of WW3
which fit pretty well with the existing forecast. Also,
graphically, checked with the Navy display as well. Both indicate
an increase in combined seas of around 10 foot on Sunday, which
would bring us to small craft advisory levels, if the frequent
gust criteria of 22 knots or more don`t trigger this advisory
earlier into the weekend. Winds will be right out of the east, so
you may get some lee side protection.


.Eastern Micronesia...
Trade winds prevail across the region with 00Z ASCAT indicating
strong trade winds just north of 10N from 150E to the dateline. A
surface trough is located east of Majuro with scattered showers and
isolated thunderstorms.

Trade winds increase across the region Friday through early next
week. The trough just east of Majuro will move through tonight with
the inter-tropical convergence zone (ITCZ) establishing just south
of Majuro on Friday. It is likely this feature will drift north at
times, delivering an increase in showers late Saturday and Monday
possibly. For Pohnpei and Kosrae, expect a breezy and showery next
several days as convergence lingers around 5N to 7N. With the steady
trades, showers will be transient and expect periods of sun at times.

Main adjustment was for the marine forecast...00Z ASCAT, upstream
altimetry, and latest WW3 guidance all suggest a slight delay with
onset of 10 foot seas. Seas hazardous to small craft is likely for
Pohnpei and Majuro, with Kosrae being a borderline event. A high
surf advisory is likely this weekend for east and north facing reefs
of Kosrae. Wave run-up forecasts from PacIOOS suggest inundation is
possible across the Marshalls Dec 14 through Dec 17 for areas
susceptible to wave energy from the north and northeast.


.Western Micronesia...
Trade-wind flow prevails for the tropical West Pacific north of 5N.
Expect trade winds to increase another notch Friday, and again on
Saturday/Sunday. Disturbances riding along on the trade winds will
increase showers at times for Chuuk and Yap...perhaps Saturday for
Chuuk and late Sunday for Yap. That said, the main action should
stay farther south near trade-wind convergence just north
of the near-equatorial trough encourages more showers.

The stronger trade winds along and north of 10N will raise seas and
surf across the region, especially for Chuuk and Yap. Surf will
likely become hazardous along north and east facing reefs of Chuuk
this weekend and Yap early next week. Palau will see elevated surf
but heights are not a shoe-in for a high surf advisory at this time.


Marianas Waters...None.


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