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Hawaiian Islands Synoptic Discussion and Guidance

791
FXHW60 PHFO 240632
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
832 PM HST Tue Jul 23 2019

.SYNOPSIS...
High pressure northeast of the state will keep moderate to locally
breezy trade winds in place through early next week. Rather dry
conditions will prevail through the remainder of the work week
with showers limited primarily to windward and mauka areas. Trade
wind showers are expected to increase over the weekend into early
next week as an upper level trough approaches and eventually moves
over the island chain.

&&

.DISCUSSION...
Currently at the surface, a trough of low pressure is located
around 425 miles west-southwest of Kauai, while a 1027 mb high is
centered around 1100 miles northeast of Honolulu. The resulting
gradient is producing moderate trade winds across the island chain
this evening. Infrared satellite imagery shows mostly cloudy skies
over Kauai, with clear to partly cloudy skies most areas from Oahu
eastward to the Big Island. Radar imagery shows a few light
showers moving into windward sections of the Big Island, with very
little if any shower activity across the remainder of the state.
Main short term concern revolves around rain chances.

Model solutions are in good agreement over the next week, showing
high pressure holding in place to the north and northeast of the
state, with a few weak troughs of low pressure passing by to the
south of the island chain. Aloft, upper level ridging will build
over area tonight and Wednesday, then hold in place over the state
through Friday. The upper ridge will begin to break down Friday
night and over the weekend as an upper level trough approaches
from the east. This upper level trough will then move over the
islands early next week.

As for sensible weather details, typical trade wind weather is
expected to hold in place through early next week, with trade
wind speeds remaining in the moderate to locally breezy range.
Very dry conditions are expected through the end of the work week,
with showers limited primarily to windward and mauka areas. The
airmass appears to moisten up a bit this weekend as the upper
ridge breaks down, so we should see a slight uptick in trade wind
showers as a result. Trade wind shower activity could increase in
both coverage and intensity early next week as the upper level
trough moves overhead. Overall however, no significant rainfall
is expected through the period.

&&

.AVIATION...
Strong high pressure northeast of the state will maintain locally
strong east to northeast winds across the islands. AIRMET TANGO
is in effect for moderate turbulence lee of the mountains.

A surface low to the west will track slowly northwest. Thick
layered clouds associated with the low cover Kauai, but
conditions are expected to slowly improve from the east.

Low topped stratocumulus embedded in the trade wind flow will
impact mainly east facing slopes and coasts bringing ISOL MVFR
conditions in passing showers.

&&

.MARINE...
A trough located just west of the offshore waters is producing
scattered thunderstorms over the far western offshore waters. This
is expected to continue through tonight and linger through
Wednesday as the trough slowly moves northwest and away from the
state. Meanwhile, high pressure far north of the state will
maintain fresh to locally strong easterly trades across the
coastal waters through the weekend. A weak low pressure system
passing south of the Big Island Wednesday night into Thursday may
bring an increase in showers around the waters of Big Island and
possibly some isolated thunderstorms over the southern offshore
waters.

The current Small Craft Advisory remains in effect through
Wednesday and will likely be extended through the second half of
the week as strong trades continue across the typical windy areas
around Maui and the Big Island.

Choppy surf will continue along east facing shores each day due
to the trades locally and upstream of the islands. A combination
of small southwest and southeast swells will continue to provide
small surf along south facing shores through the week. Surf
heights are expected to remain below advisory levels along all
shores through the foreseeable future. See the Collaborative
Nearshore Swell and Wind Forecast, SRDHFO, for additional details
on swell sources.

&&

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

&&

$$

DISCUSSION...Jelsema
AVIATION...Morrison
MARINE...Kino

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