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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 060631

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Fri Jun 5 2020

Breezy trade winds will ease somewhat Sunday and Monday, and then
strengthen again next week. The trade winds will deliver increasing
clouds and showers to windward areas beginning later tonight, likely
continuing through Saturday night.


After a mostly dry day statewide, latest satellite images show an
area of increased showery and stable low clouds approaching the
islands from the E. Model guidance continues to indicate a weak 700
mb trough supporting this area, with the trough expected to sharpen
as it moves W over the islands through Saturday night. PWAT is
expected to increase to 1.4" (currently near 1.0"), with the net
effect being an increase in mainly windward showers. Otherwise, the
forecast philosophy presented earlier is congruent with latest model

Clouds and passing showers riding moderate/breezy trade winds
will mainly affect windward and mountain areas, with an occasional
shower reaching leeward locations. High pressure centered far
northeast of the islands extends a ridge along 30N across the
central Pacific, providing our island trades. Over the weekend the
high will move slowly E turning our winds slightly S of due E Sunday
and Monday. This alignment will allow for lighter winds over leeward
sections of Kauai and Oahu with the Big Island and Maui County
partially blocking the easterly trade winds. Winds over the eastern
islands look to remain at moderate to locally fresh speeds.

Afternoon soundings from Lihue and Hilo depict a 8 degree F
temperature inversion between 6000 and 9000 feet. This inversion
is capping the trade winds showers, and visible satellite imagery
bears this out showing clouds banking up along the windward
slopes. The strong inversion is expected to remain in place into
the weekend with some weakening expected Sunday and early next
week as a midlevel trough moves overhead. Trade showers and cloud
top heights may increase a notch in response to the weaker
inversion. All that being said, trade wind weather will continue
into the foreseeable future with small/moderate fluctuations in
wind speeds and rainfall.


High pressure to the northeast of the state will once again generate
moderate to occasionally breezy easterly trades tonight. Expect
scattered showers along the windward coasts and with occasional
showers over the elevated terrain. Periods of MVFR conditions will
likely accompany this aforementioned shower activity due to low
ceilings and reduced visibility.

AIRMET TANGO remains in effect for over and immediately south
through west of mountains below 8000 feet for tempo moderate


A ridge of high pressure is roughly 600 nm north of Kauai this
evening. The ridge belongs to a high located 840 nm northeast of
the islands. These two features will maintain breezy to locally
strong trade winds through the first half of the weekend over the
eastern end of the state. A Small Craft Advisory (SCA) is in
effect to until late Saturday afternoon for the typically windy
areas of Maui County and south of the Big Island. Another
extension to this SCA is possible, that is through Sunday.

A front passing far to the north will bring the ridge a little
closer to the islands, so by Sunday night or Monday, the trades
would be weaker, resulting in the cancellation of the SCA. This
lull could be short-lived, with SCA likely returning Monday night
to the typically windy waters, and continuing through at least
the middle of next week. This comes about as the front falls
apart, allowing the ridge to move north and the expansion of trade
winds.long- period pulse fills in by Saturday

The latest south swell continues to trend down, although a
reinforcing small but long period swell is expected to fill in by
Saturday. This will result in surf at about summer time average
through the weekend. This will begin lowering Sunday into early
next week. A small swell from the Tasman Sea is expected by
Wednesday. A mid-size bump is expected for our south facing

Surf along east facing shores will remain small but choppy on
Saturday. Surf could be a foot less between Sunday and Monday,
due to the weaker trades locally, but will be building back up
as the stronger trades return by the middle of next week.
The north facing shores will have small surf through the weekend,
and into next week.


Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.




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
Send comments to: Ryan Lyman