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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 240644

Area Forecast Discussion
National Weather Service Honolulu HI
844 PM HST Fri Aug 23 2019

A high north of the area will move northeast slowly and maintain locally
breezy easterly trade winds through the weekend. A band of showery low
clouds will move west over the smaller islands tonight. Another area
of showers may spread over the area tomorrow. Winds will weaken next
week as the high moves farther away and rainfall will likely be sparse.


The latest surface analysis shows a 1025 mb surface high about
1000 miles north of the area near 36N165W. The pressure gradient
south of the high is maintaining locally breezy easterly trade
winds over the main Hawaiian Islands.

A 220 mile wide area of showery low clouds is moving west at about
15 mph across the islands. As of 8 PM, the west edge of the clouds
was over Kauai and the east edge was over Maui. Radars show
numerous showers in this cloud area. As the cloud area continues
moving west, showers will subside over Maui County this evening,
Oahu later tonight and Kauai County early Saturday morning.
The global models show an area of increased moisture moving
toward the islands from the southeast that is likely to produce
another increase in showers, especially for the windward side of
the Big Island, on Saturday.

The global models are in good agreement showing the high north of
the area moving northeast slowly. As the high moves away, the
pressure gradient over the islands will become looser and the
trade winds will weaken. Wind speeds will likely become gentle to
moderate by Tuesday and remain at that strength through the rest
of the week. Moisture will remain rather low and ridging aloft
will keep the atmosphere stable so rainfall will be sparse through
next Friday.


A high north of the Hawaiian Islands will keep moderate to breezy
trade winds in the forecast through the weekend. A low level
trough passing through the western half of the state tonight will
produce periods of MVFR ceilings and scattered to numerous showers
from Molokai to Kauai. These low cloud ceilings and showers will
favor the north and east slopes of the western islands, and
gradually decrease in coverage from east to west through the night.

Two AIRMETs remain in effect. AIRMET Sierra for Tempo Mountain
Obscuration along north and east slopes of Molokai, Lanai, Oahu,
and Kauai. AIRMET Tango for low level Moderate Turbulence south
through west of all islands. AIRMET Sierra will decrease in
coverage later tonight, while AIRMET Tango will likely remain in
effect through at least Saturday.


High pressure to the north will maintain moderate to locally strong
easterly trades through the weekend. A Small Craft Advisory (SCA)
is posted through Sunday for the windy waters around Maui and the
Big Island. The high will move northeast slowly, relaxing the
pressure gradient over the area early next week, resulting in
lighter trades toward the middle of next week.

A surface trough, oriented northeast through southwest across the
far northwestern offshore waters this evening is forecast to move
west the rest of tonight, moving west of the far west and northwest
offshore waters by sunrise Saturday.

Only background south swell energy is expected over the weekend
into early next week. A larger, longer period southwest swell is
expected to arrive Tuesday and peak Wednesday or Thursday near
advisory levels.

A northwest swell will maintain small surf along the north and
west facing shores over the weekend. Meanwhile, the stronger
trades on tap for the weekend will lead to a slight rise in the
surf along the east facing shores. This trade wind swell will
trend lower the middle of next week as the trades become weaker,
resulting in lower surf. The strong trades will cause rough and
choppy water conditions, especially along east facing shores over
the weekend and into early next week.


Small Craft Advisory until 6 PM Sunday for Maalaea Bay, the
Pailolo and Alenuihaha Channels and waters south of the Big



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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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