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Hawaiian Islands Synoptic Discussion and Guidance

190
FXHW60 PHFO 150626
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
826 PM HST Fri Aug 14 2020

.SYNOPSIS...
Breezy trade winds will prevail into Saturday night, then trend
down Sunday through the upcoming week as high pressure to the
northeast weakens. Clouds and showers will favor windward and
mountain areas each day, especially through the overnight and
early morning periods as pockets of moisture move through. Shower
coverage may increase by the middle of the upcoming week as an
upper disturbance moves into the area.

&&

.DISCUSSION...
Latest surface analysis and satellite imagery showed the
subtropical ridge anchored north of the islands and a weak trough
moving over the eastern end of the state this evening. Trade wind
convergence into this trough has led to a band of clouds and an
increase in windward shower coverage for Maui County and the Big
Island. Rain gages reflected this and showed only light
accumulations over these windward areas. Expect this trend to
continue into early Saturday morning, with windward shower
coverage increasing from east to west as this feature moves
through.

Guidance has initialized well with the current pattern and shows
trades trending up Saturday through Saturday night as the
aforementioned weak trough continues westward and the gradient
tightens over the region between the ridge to the north and low
pressure passing far to the south. Drier air trailing this weak
trough combined with an upper ridge nosing westward over the region
will support decreasing windward shower coverage from east to west
through the weekend.

Guidance shows the pressure gradient relaxing Sunday into early next
week as the area of low pressure to the south continues westward and
a weakness in the subtropical ridge forms far north of the state as
a backdoor front drops southward over the northern Pacific. An upper
trough associated with this surface feature is forecast to drop
farther south over the islands by midweek. If this materializes, a
slight increase in windward shower coverage will become a
possibility, especially as pockets of moisture move through.

&&

.AVIATION...
A band of low clouds and showers will move though the islands
from east to west tonight. MVFR cigs/vsbys can be expected in
windward areas as these showers move through, with VFR conditions
generally prevailing in leeward areas. Drier conditions and
moderate to breezy trade winds are expected to develop statewide
by mid morning Saturday.

AIRMET Sierra is in effect for mountain obscuration across
windward sections of the Big Island, Maui, Molokai and Oahu.
Mountain obscuration will likely spread to Kauai later tonight,
while conditions over the Big Island should gradually improve.

AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of the terrain of Maui and the Big Island. This
AIRMET will likely be expanded to the entire island chain later
tonight.

&&

.MARINE...
Moderate to locally strong trade winds will be blowing through the
main Hawaiian Islands through Saturday night as the pressure
gradient tightens over the islands in response to an area of low
pressure passing far to the south. A Small Craft Advisory (SCA) has
been posted for the typical windier waters Maui County and the
Big Island through early Sunday morning. Trades may briefly bump
up a notch to locally strong Monday night, then settle down to
moderate speed by Thursday.

Surf along east facing shores will hold steady into the weekend
just under the advisory level of 8 ft as a moderate northeast
swell moves through. The north facing shores exposed to this
swell will also see a small increase in surf. Surf will gradually
ease Sunday into early next week as the swell subsides and the
trade winds become weaker. A small easterly swell is still
possible this weekend, generated by the former TC Elida in the
eastern Pacific, especially for the eastern end of the state.

A small south- southwest swell from the south will cause surf to
gradually trend up Sunday into early next week. A reinforcement
swell from the same direction arrives Monday night through
Tuesday, then hold through midweek before easing.

&&

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

&&

$$

DISCUSSION...Gibbs
AVIATION...Jelsema
MARINE...H Lau

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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