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Hawaiian Islands Synoptic Discussion and Guidance

518
FXHW60 PHFO 120551
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
751 PM HST Mon Nov 11 2019

.SYNOPSIS...
Light trade winds will prevail through Wednesday, then shift out
of the south Thursday through Friday as a cold front and upper
disturbance approach from the northwest. Clouds and showers will
favor the typical windward and mauka locations through Wednesday,
except over leeward areas where localized sea breezes develop
through the afternoon and early evening periods. Rain chances will
trend up later in the week and into the weekend as moisture rises
ahead of the front and as a weak trough moves into the area from
the east.

&&

.DISCUSSION...
Water vapor imagery showed an upper ridge nosing eastward over the
state and a potent shortwave trough racing eastward over the central
Pacific. Latest surface analysis showed high pressure centered
several hundred miles north of the area and a cold front associated
with the upper trough extending south-southwest from a 971 mb low
pressure system centered south-southeast of the Aleutians to Midway.
A cloud band was shown lurking from east to west within a couple
of hundred miles to the north that was drifting southward. Light
background trades south of this lingering band are holding across
the islands, which will give way to another night with land
breeze conditions. Shower coverage should remain limited with
quiet conditions prevailing overnight.

The latest short-term (through Wednesday) guidance remains in good
agreement and depicts mostly dry and stable conditions with light
background trades holding. The cloud band lurking to the north,
however, could bring some additional showers to windward areas and
a slight increase in the trades by Wednesday, if it drifts far
enough south into the area. Otherwise, the best rainfall chances
will continue to favor interior and leeward locations through the
afternoon and early evening hours due to peak heating and
localized sea breezes.

For the extended period (Thursday through the weekend), guidance
shows the progressive pattern continuing. The ridge is forecast to
break down to the north as the potent shortwave trough digs
southeastward and drives a cold front into the area. As this
scenario evolves, a weak trough approaching from the east-southeast
is forecast to move over the eastern end of the state late Friday
through Saturday. Although it remains too early to pinpoint any
details, increasing moisture and instability associated with these
synoptic features will likely translate to increasing rainfall
chances Friday through the weekend statewide.

&&

.AVIATION...
A light easterly wind pattern will become modified by land and sea
breezes over each island, leading to a variable light wind
pattern through Tuesday. Clouds will develop over island mountain
and interior sections during the daylight hours with isolated to
scattered showers developing in the afternoon and early evening
hours. Overnight land breezes will clear out cloud cover over
island airfields each night.

No AIRMETS in effect and none are forecast.

&&

.MARINE...
Generally east winds will be experienced over the coastal waters
for another day, but look for more light and variable winds for
the middle of the week. Beyond that, southerly flow is expected,
with winds remaining well below Small Craft Advisory (SCA) levels.

The current north-northwest swell peaked earlier in the offshore
buoys, and appears to have peaked at some of the near shore buoys
in the afternoon. Surf did exceed advisory levels, so a High Surf
Advisory (HSA) was issued just before noon. Anticipating the surf
to be on the decline tonight, so the HSA goes through early
Tuesday morning, with surf expected to be below advisory levels
by day break, and then continue to gradually ease into the middle
of the week.

Another north-northwest swell being generated by a developing
hurricane-force low north of Midway along the date line is
expected to reach the islands Thursday, and peak at advisory
levels Thursday night, then hold through the end of the week.
Another northwest swell is expected to arrive over the weekend,
raising surf to near warning levels.

The current south swell continues to subside, so expect surf to
gradually diminish. A small south-southwest swell is expected
Thursday night into the weekend. Surf along east facing shores
will remain small with light winds near and upwind of the
islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Tuesday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu Koolau-
Olomana-Molokai-Maui Windward West-Maui Central Valley- Windward
Haleakala.

&&

$$

DISCUSSION...Gibbs
AVIATION...Bohlin
MARINE...Kinel

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



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