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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 280631
Area Forecast Discussion
National Weather Service Honolulu HI
831 PM HST TUE SEP 27 2016
Locally breezy trade winds will maintain a somewhat stable
rainfall pattern focusing showers across windward slopes through
Friday. Showers are expected to increase during the weekend as
deeper low level moisture moves over the islands and a mid to
upper level trough strengthens near the state.
Moderate to locally breezy trade winds and a rather typical
pattern of mainly windward and mauka showers will prevail into
Friday. A surface ridge will hold north of the islands, producing
only minor fluctuations in the trades. Broad mid to upper level
ridging overhead will maintain somewhat stable conditions, with
the inversion hovering around 6000 to 8000 ft for most of this
time. The GFS and the ECMWF are showing a weak mid level trough
passing over the islands late Wednesday and Wednesday night that
may cause an uptick in showers. Otherwise, expect showers to be
largely confined to windward slopes.
Shower chances will increase heading into the weekend. The GFS
and ECMWF both show a nearly east to west oriented upper level
trough (referred to as a tropical upper tropospheric trough, or
TUTT) setting up on Friday just north of the islands and gradually
strengthening through the weekend. The models are showing a mid
to upper level low developing along the western end of the TUTT,
but they differ on the location, with the GFS farther west than
the ECMWF. During this time, deeper low level moisture should be
moving in from the east, leading to a likely increase in showers.
The position of any future upper level low will have implications
for heavy shower potential, and for now, uncertainty is too high
to include mention.
The National Hurricane Center in Miami is issuing bulletins on
Tropical Storm Ulika, located over 1100 miles east southeast of
Hilo. A then weakening system is likely to move west of 140W,
back into the Central Pacific Hurricane Center area of
responsibility, in a couple of days. Some low level moisture from
the remnant of Ulika could affect the islands next week, but it is
too far away include in the local forecast.
High pressure north of the state will keep a moderate to breezy
trade wind flow in place through Wednesday. Predominantly VFR
conditions are expected at the TAF sites, with brief MVFR
cigs/vsbys possible in passing -SHRA across windward and mauka
AIRMET Tango is in effect for low level turbulence over and
downwind of the mountains. Conditions are expected to remain in
place through Wednesday.
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 will likely remain
strong enough for the SCA to stay up.
A small north 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-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Public and Marine...Wroe
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office