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Temp5.0 C
RH9 %
WindNNE 11 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

777
FXHW60 PHFO 181341 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
341 AM HST Sat Sep 18 2021

.SYNOPSIS...
Breezy trades will continue through the weekend, with a slight
easing expected Sunday night and Monday. The trades will then
increase back to breezy levels Tuesday and Wednesday, before
dropping a notch late next week. Fairly typical trade wind weather
will prevail through the forecast period. Showers will favor
windward and mauka areas, particularly at night and during the
early morning hours, with an occasional shower spilling over into
leeward communities from time to time.

&&

.DISCUSSION...
Currently at the surface, a 1028 mb high centered around 1125
miles north of Honolulu, is driving moderate to breezy trade winds
across the island chain early this morning. Infrared satellite
imagery shows a mix of high and low clouds resulting in partly to
mostly cloudy conditions across the state. Radar imagery shows
scattered light showers moving into windward areas, with a few
showers spilling over into leeward communities from time to time.
Main short term concerns revolve around trade wind trends and
rain chances during the next few days.

High pressure to the distant north will shift eastward this
weekend, keeping rather breezy trade winds in place across the
island chain. The trades should ease into the moderate range
Sunday night through Monday night as a front passes by far to the
north of the state. A trough of low pressure will then slide by
to the south of the islands Tuesday and Wednesday, and this should
boost the trades back to breezy levels once again. A slight easing
of the trades is possible late next week as a new front approaches
from the northwest.

As for the remaining weather details, the most recent model
solutions suggest that an areas of disturbed weather far to the
southeast of the islands, may send an area of enhanced moisture
toward the Big Island Monday night through Tuesday night. If this
occurs, rain chances will likely need to be increased and
thunderstorms may need to be added to the forecast as well. Given
that this is only a recent trend however, will keep the forecast
in line with previous model runs and forecast packages, which
suggest this deep moisture will slide by to the south of the
island chain. As a result, we expected a fairly typical trade wind
weather pattern to prevail throughout the forecast period.
Showers will favor windward and mauka areas, particularly at night
and during the early morning hours, with a few showers
occasionally reaching leeward areas due to the strength of the
trades.

&&

.AVIATION...
Breezy to strong trade winds will continue to produce low-level
turbulence across the state downwind of the island terrain
through much of the weekend. AIRMET Tango remains in effect for
this. MVFR CIGS/VSBYS are possible in and around passing showers
focusing over windward coasts and slopes. Otherwise, VFR
conditions will prevail, with limited showers expected over
leeward areas.

&&

.MARINE...
High pressure north of the state will maintain fresh to locally
strong trade winds this weekend. Last night's ASCAT satellite
pass over the eastern third of the state continued to verify
advisory level winds across the Alenuihaha channel and off of
Big Island's South Point. The eastern movement of the high the
next few days will provide very little change to the Central
Pacific pressure gradient. This will result in little variance to
these fresh to locally strong winds. Today's Small Craft Advisory
(SCA) has been reconfigured to include all waters except the
windward Kauai, Oahu and Big Island waters. Tonight through early
Sunday's SCA drops off the western Kauai waters and the Kauai
Channel while Sunday's SCA pares the area further east to just
cover the typically windier zones around Maui County and waters
south of Big Island.

Medium period background southwest to south swells will hold surf
along the south facing shores to slightly below normal summertime
averages into early next week. Small, long period south swell
energy originating from recent Southern Hemispheric gales
southeast of New Zealand is timed to arrive around mid week.
These swells may bump surf back up to near summertime averages
during the second half of the week. A small, medium period
northwest swell is expected to reach the northwest islands later
today and travel through the chain Sunday. These swells will lift
north and west facing shore surf from near flat to possibly chest
high Sunday. A series of slightly larger, medium period northwest
swells emanating from a couple of eastern passing North Pacific
gale lows will come across the islands next week. A few days of
fresh trades over and upstream of the region will support choppy
wind waves along most eastern exposures through the middle of next
week.

&&

.FIRE WEATHER...
Gusty winds in combination with dry fuels and low relative
humidity levels will result in elevated fire danger this
afternoon. Any fires that develop will spread rapidly and be
difficult to control. Therefore, a Red Flag Warning remains in
effect for leeward sections of Kauai, Oahu, Molokai, Maui, Lanai
and the Big Island until 6 PM this evening.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 6 PM HST this evening for Kauai Leeward-
Oahu South Shore-Waianae Coast-Oahu North Shore-Central Oahu-
Waianae Mountains-Molokai Leeward-Lanai Makai-Lanai Mauka-Maui
Leeward West-Maui Central Valley-Leeward Haleakala-Haleakala
Summit-Kona-South Big Island-Kohala-Big Island Interior.

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

Small Craft Advisory until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Leeward Waters-Kauai Channel.

Small Craft Advisory until 6 AM HST Sunday for Oahu Leeward
Waters-Kaiwi Channel-Maui County Windward Waters-Maui County
Leeward Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Gibbs
MARINE...Blood

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