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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 271950
Area Forecast Discussion
National Weather Service Honolulu HI
950 AM HST TUE SEP 27 2016
A surface high far north of the area will move north through mid-
week, then back south through next weekend. A ridge aloft will
remain over the islands through Friday. A trough aloft may affect
weather for the islands starting over the weekend.
Satellite loops through 900 AM show overcast clouds over the
windward side of the Big Island, scattered to broken clouds over
windward areas of the other islands and only isolated clouds
elsewhere. Radars are showing only isolated light showers upstream
of the islands.
The global models are in good agreement showing moderate to breezy
trade winds and stable conditions through the day on Friday. The
trade winds will push showers over windward areas, especially during
the nights and mornings. Leeward areas of the smaller islands will
be relatively dry while there will be afternoon clouds and showers
over the leeward side of the Big Island.
Both the GFS and ECMWF show an east northeast to west southwest
trough aloft trough, the kind often called a tropical upper
tropospheric trough, or TUTT, deepening north of the islands
starting Friday. Both models also show a low aloft developing
northwest of Kauai on Saturday. Beyond that, the models diverge
significantly and at this point it is hard to know which one will be
better. In either case, the atmosphere over the islands is likely to
become more moist and unstable over the weekend. Both models show
moisture from the remnant of Ulika moving over the islands moving
over the islands over the weekend. If the development of the trough
aloft and the arrival of the tropical moisture match closely enough,
there could be a period of wet weather over the islands.
The Central Pacific Hurricane Center in Honolulu has been issuing
bulletins on Tropical Storm Ulika. This system is over 1100 miles
east southeast of Hilo and is moving north slowly. The system is now
east of 140W, so the National Hurricane Center will be issuing the
bulletins on the system. The cyclone is not expected to affect
weather in the islands for the next several days.
VFR will prevail but ENE trade winds may produce isolated MVRF
conditions over windward areas, especially on the Big Island.
Breezy trade winds will persist through at least the next 24 hours.
Expect AIRMET TANGO to remain up for low level turbulence to the lee
of the mountains.
A Small Craft Advisory (SCA) is in effect for the windy areas around
the Big Island and Maui. Both the GFS and ECMWF both show winds
weakening over the next 24 hours, but the winds may remain strong
enough for the SCA to stay up.
A small northwest swell will continue through tomorrow before fading
away. Surf will remain well below the advisory levels on all shores
for the next several days. Please see the Collaborative Surf
Discussion in the Marine section on our web site for details.
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay, the
Pailolo and Alenuihaha Channels and waters south of the Big Island.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office