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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 190128
Area Forecast Discussion
National Weather Service Honolulu HI
328 PM HST Tue Feb 18 2020
A ridge of high pressure north of the state will bring windy
trade wind weather over the next couple of days, then taper off
by this weekend. Clouds and passing showers will favor windward
and mountain areas, with showers occasionally passing over to leeward
sides of the smaller islands. Winds will then veer southeasterly
as a weak cold front approaches and dissipates near the islands.
A strong high pressure system north of Hawaii will drive windy
trades over the next couple of days. A Wind Advisory is posted
for areas of Maui County and the Big Island through Thursday. Kauai
and Oahu have been added to the advisory for Wednesday and Wednesday
night. See NPWHFO product on our website for more information.
Strongest winds will affect exposed areas such as mountain ridges
and points between the islands. Strong gusts are expected in
leeward areas downslope of the mountains.
Soundings from 00Z at Hilo and Lihue show a dry and stable atmosphere
with inversion height between 6-8 kft in elevation. Showers carrying
in with the trades will focus over windward and mauka areas, but
will occasionally pass over leeward sides of the smaller islands
at times. Rainfall accumulation is not expected to be significant.
Trade winds will weaken around Friday and veer southeasterly this
weekend as a fast moving, but weak, cold front approaches. As the
winds veer, showers will favor southeast slopes of Maui and the
Big Island with the rest of the state getting a convective weather
pattern setting up. By Sunday, afternoon sea breezes will bring
clouds and showers to interior sections while nighttime land
breezes clear them out. The front will dissipate Monday with high
pressure building to north ushering in trade winds. The trades may
focus some of the remnant clouds and showers associated with the
dissipated front back over the island chain through the middle of
Breezy to windy trade winds are in the forecast for the next
couple of days with the winds increasing further through Thursday.
AIRMET Tango is in effect for tempo moderate low level turbulence
below 8,000 ft for areas west through south of the mountains.
AIRMET Tango is also in effect for strong surface winds of 30
knots or greater, mainly over the water and land areas where
terrain accelerates wind speeds. Both of these AIRMETs are
expected to continue for the next few days.
The shower and cloud activity will be sporadic and mostly light with
a focus on windward areas, though strong winds could push the occasional
shower over onto leeward areas. This will result in occasional periods
of MVFR conditions over windward areas, but shouldn't be widespread
or lasting enough to warrant AIRMET Sierra for mountain obscuration.
Expect VFR conditions for the rest of the state.
High pressure is currently centered far NW of the state,
resulting in breezy to locally strong trade winds across the
area. Winds will gradually increase over the next day or so as the
high moves steadily eastward. A Small Craft Advisory (SCA) is
currently posted for all Hawaiian Coastal Waters. Also, the Gale
Watch has been replaced by a Gale Warning for the the windier
zones around Maui County and the Big Island, beginning midnight
tonight and extending through Thursday afternoon. The high will be
far northeast of the islands by Saturday, resulting in the trades
gradually diminishing across the area. A front approaching the
islands from the NW will cause the trades to become SE over the
western end of the island chain by early in the weekend.
The current northwest swell will continue to lower, but will be
reinforced by a small northwest swell Wednesday. This swell will
peak Wednesday night or Thursday, then gradually lower through
Friday. A slightly larger northwest swell is expected to arrive
late Friday and Friday night, peak Saturday, then lower slowly
Sunday and Monday.
The strengthening trade winds will cause a rise in the trade wind
swell, resulting in elevated surf along the east facing shores
between Wednesday and Thursday night, likely reaching the High
Surf Advisory threshold of 8 feet. But with the softening of the
trades starting Thursday into Thursday night, expect the surf to
lower slightly each day into the weekend. A series of small, out
of season south swells can also be expected through the rest of
the week, including the upcoming weekend.
Wind Advisory from 6 AM Wednesday to 6 AM HST Thursday for Kauai-
Wind Advisory until 6 PM HST Thursday for Molokai-Lanai-
Kahoolawe-Maui Windward West-Maui Leeward West-Maui Central
Valley-Windward Haleakala-Leeward Haleakala-South Big Island-Big
Island North and East-Kohala.
Small Craft Advisory until midnight HST tonight for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Gale Warning from midnight tonight to 6 PM HST Thursday for
Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters-Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Thursday for all remaining
Hawaiian Coastal Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office