Current Conditions
Temp5.0 C
RH61 %
WindNE 15 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

136
FXHW60 PHFO 221955
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
955 AM HST Tue Aug 22 2017

.SYNOPSIS...
An upper level low northwest of the islands will continue to bring
the chance for locally heavy showers, and the slight chance of
thunderstorms today. Otherwise, building trade winds will focus
clouds and showers over the windward areas. Breezy trade winds
and drier conditions will return Wednesday and continue into the
upcoming weekend as high pressure strengthens north of the state.
Trade winds are forecast to relax by the end of the upcoming
weekend as high pressure weakens to the north.

&&

.DISCUSSION...
An upper level low is about 275 miles northwest of Kauai this
morning based on water vapor imagery. This upper level feature has
helped to destabilize the atmosphere over the region over the
last few days. The low is forecast to continue to move to the
west/west northwest over the next couple of days. Its influence on
our local weather should diminish over the next 12 to 24 hours as
it moves away from the area.

During the pre-dawn hours, there was a thunderstorm just south of
Niihau. Due to the proximity to the upper level low, thunderstorms
remain a possibility near Kauai and Niihau today. Build-ups on the
Big Island will also be possible, mainly during the afternoon
hours. Across the state, building trade winds will focus clouds
and showers over windward areas, but the instability provided by
the nearby upper level low could mean heavier showers at times
today.

A surface high building far north of the islands will maintain the
trade wind flow into the weekend. Moderate to locally breezy
trades are expected, so while most shower activity will be focused
over the windward and mauka areas, don't be surprised if a few
showers reach leeward areas. Winds will likely drop a touch over
the weekend as the high begins to weaken.

&&

.AVIATION...
Over the next 24 hours, a surface high will build far N of the
area, while a low aloft NW of Kauai moves W. This will lead to
strengthening trade winds and a reduction in shower coverage and
intensity. In the meantime, the island atmosphere remains
sufficiently unstable to support the development of +SHRA/+TSRA
which have the potential to bring IFR CIG/VIS.

Most likely location for MVFR/IFR conditions in the short term is
over and near the Big Island and windward Maui, where AIRMET
SIERRA remains in effect for mountain obscuration. The increasing
winds have also prompted the issuance of AIRMET TANGO for low-
level turbulence.

&&

.MARINE...
With trade winds on the increase, a Small Craft Advisory (SCA) is
currently in effect for the typically windier zones around Maui
County and the Big Island. The SCA is in effect through Thursday
afternoon.

An upper level low has been heading west away from the islands,
but will still likely produce isolated thunderstorms over coastal
and offshore waters through the day. The highest risk is for the
waters in the west half of the forecast area. More stable and
drier conditions are expected Wednesday and through the second
half of the week.

East-facing shores should see a slight increase in surf heights
as the trade winds rebuild today. A longer period east swell may
also arrive during the second half of the week as a result of
tropical cyclone activity in the eastern Pacific. South-facing
shores may see a slight increase in surf this weekend from a swell
train that originated from a Tasman Sea gale. A small background
southeast swell is also expected through the forecast period.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$


DISCUSSION...M Ballard
AVIATION...Birchard
MARINE...Kinel

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office