Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

FXPQ60 PGUM 162215

Area Forecast Discussion
National Weather Service Tiyan GU
815 AM ChST Sun Feb 17 2019

.Marianas Synopsis...
Andersen Air Force Base Doppler weather radar shows almost no showers
within the Marianas waters. The VAD wind profile indicates northeast
winds of 17 to 22 knots through the lowest 6 thousand feet of the
air. The buoys reveal 7 to 9 foot combined seas from east-northeast
composed of everything from 7 second wind waves to 17 second swell,
with the peak being around 9 to 10 seconds.


For the next few days at least, the Marianas remain locked in a dry
trade-wind regime with only spotty light showers. Near the end of
this week, the winds of change could be blowing though, as a tropical
disturbance southeast of Kosrae moves in our general direction. Most
likely it will pass south of Guam...the age old question, will it be
just south of well south...will take at least another couple of days
to get a good idea. The effects of this system (or the lack thereof)
will be the big weather story this week.


Combined seas remain at 7 to 9 feet, just below small craft advisory
criteria. They will probably go back above Monday or Tuesday, so any
mariners should keep informed. Due in large part to criteria being
higher along east facing reefs, a high surf advisory will be a bit
harder to come by. Even that is likely by Thursday though. The waters
are about to get dangerous again, please beware.


.Fire weather...
The vegetation of the Marianas continues to bake in the sun with
little or no rain to relieve it. The Keetch-Byram drought index looks
like it should be around 569, only 31 away from the critical value,
and afternoon humidities seem to be turning critical now. Unless the
disturbance gives us a lot of rain, it could be time to turn the
attention to fire weather as the big problem.


.Tropical systems...
Visible satellite imagery shows a tropical disturbance centered near
2N167E. The center is displaced southeastward from the convection, so
development will be a bit slow if any at all over the next 24 hours.
The numerical models all favor it though, so it does bear watching.


.Eastern Micronesia...
Satellite shows an extensive area covered with numerous to
occasional showers and isolated thunderstorms south-southeast of
Kosrae at the turning angle of northeast to northwest winds from
between surface and 700mb and along the trough axis extending
northeastward from west of 150E to a weak tropical disturbance
southeast of Kosrae. Meanwhile, cloud remnants from diffuse shear
lines north of 10N continue to pass near Kosrae and Pohnpei. Fresh
to strong trade winds combined with the weak tropical disturbance
southeast of Kosrae will trigger increasing moisture flux well west-
southwest of Majuro and near Kosrae and Pohnpei in the coming days.
Altimetry shows combined seas on the north and south flanks of
Majuro between 8 to 10 feet but Kalo/Majuro buoy suggest seas up to
7 to 9 feet, and at Pohnpei...combined seas between 5 to 9 feet.
Currently, Advisories for surf remain in effect for both Kosrae and
Majuro, and Small Craft Advisory continues for all 3 locations as
seas remain near 10 feet or higher. It is possible that the Kalo
buoy is sheltered by Arno and is reading a foot low.

It seems the models are being precocious and developing it too early
too fast. It may take a bit of time for the predicted hazardous and
dangerous seas to materialize. There is widespread model consensus
that this thing will develop...if wrong, they are all wrong. More
likely is that they are merely too fast. That still has us wondering,
when will this actually happen...and if it will still be in our area.
Due to the uncertainty, maintained previous advisories and forecast
package. We will continue to keep an eye on this situation.


.Western Micronesia...
Trailing clouds from shear lines north of 10N are passing near all 3
locations this morning. Both Yap and Koror lies underneath dry
subsiding air which favors mainly quiet and dry weather, with only
a few showers expected. Apparently, scatterometer and RAOB from last
night indicate wind speed up to 20 kt between surface and 600 feet
over the forecast zones.

Computer models entertain the disturbance from East Micronesia to
move near Chuuk in the next two or three days, but we chose to
maintain the previous forecast package and keep showers at a
minimal. Altimetry from last night east of Yap show 6 to 8 feet and
east of Chuuk between 8 to 10 feet. For this reason, have agreed to
the previous sea forecast and there were no significant changes on
WW3 for the next few days.


GU...High Rip Current Risk through late Friday night for GUZ001>004.

Marianas Waters...None.


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