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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 300203
Area Forecast Discussion
National Weather Service Honolulu HI
350 PM HST WED JUN 29 2016
Trade winds will increase and become gusty Thursday night through
the weekend. Moisture in the trades will decrease Thursday
afternoon and night, just as the winds ramp up, and will bring less
clouds and showers through Saturday. Clouds and showers may increase
again late Sunday into Monday.
The main weather impact to the state will be gusty and locally
strong trade winds expected Thursday night through the weekend. It
looks like the trades will peak in intensity late Friday and early
Saturday with gusts approaching wind advisory level in the windiest
higher elevation spots around the state with gusts approaching 45
mph in these areas. These gusty winds are due to a strengthening
high pressure ridge north of the state. This 1034mb ridge at the
surface extends up through the mid levels of the atmosphere, thus
the easterlies will be fairly deep across the state, reaching up to
20000 feet. The airmass will be very stable starting later Thursday,
and this will serve to accelerate the winds over the island terrain.
Isolated thunderstorms developed late this afternoon over the Big
Island, near the summit of Mauna Loa. Scattered showers are also
spread across the Big Island Saddle and even upslope of Mauna Kea.
Cannot rule out additional lightning and thunder up in these high
elevation areas into the early evening. These showers will decrease
as the sun sets and upslope breeze decreases on the leeward sides.
Moisture is expected to remain above normal through much of the day
Thursday, but as drier air will work its way in from the east
Thursday afternoon, shower activity will decrease over windward
areas as well.
Some indications are in the GFS medium range guidance of increasing
tropical moisture late Sunday into Monday, moving in from the
southeast. But this will depend largely on how much moisture pools
in the trough currently near 130 West. This trough is expected to
move westward and remain south of the state, but some of the
moisture may wrap up around the north side of the trough and affect
the state. This potential forecast scenario will need to be
monitored in future model runs.
VFR will prevail across the island chain, with brief MVFR conditions
expected in windward and mauka sections. An upper level disturbance
is forecast to move to the north and northwest of the state, and may
enhance showers over the isles tonight, especially Kauai and Oahu.
An AIRMET for low level turbulence to the lee of the mountains
remains in effect.
A Gale Watch is issued for Thursday night through Saturday time
frame as the trades strengthen to gale force in Pailolo and
Alenuihaha Channels and South of the Big Island. Elsewhere, as winds
increase area-wide, choppy seas and gusty winds will make difficult
for small craft across much of the state, especially Friday and
Surf will remain below advisory levels along all shorelines the next
couple of days. As trade winds strengthen late in the week, surf
along E facing shores will increase, and a high surf advisory
will likely be necessary over the weekend.
Gale Watch from Thursday evening through Saturday afternoon for
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Small Craft Advisory from 6 AM to 6 PM HST Thursday for Big Island
Leeward Waters-Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-Pailolo
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office