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Hawaiian Islands Synoptic Discussion and Guidance

913
FXHW60 PHFO 240152
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
352 PM HST Thu May 23 2019

.SYNOPSIS...
A moderate east southeast wind flow will prevail across the area
through tonight. Warm and humid conditions will continue with
some relief as the winds shift east Friday into the Memorial Day
weekend. Winds will weaken and shift east southeasterly Tuesday
and Wednesday next week.

&&

.DISCUSSION...
A 1033 mb high is centered about 1500 miles northeast of the state.
A stationary front is located about 450 miles northwest of Kauai
with a cold front 700 miles northwest of Kauai advancing towards
the stationary front. This current synoptic setup is driving
moderate east southeast winds across the islands this afternoon.
Under this wind direction, the Big Island and Maui are causing
some degree of blocking of the background winds allowing for a
daytime sea breeze and nighttime land breeze to take over for
areas downstream. Dew points and relative humidity levels are also
running a bit higher due to the more southerly component to the
wind direction than the typical trade winds. Visible satellite
shows low clouds over most of the islands this afternoon with just
a few showers on radar. These clouds and showers will decrease
through the evening hours as land breezes set in.

The cold front to the northwest will merge with the stationary
front. The intrusion of the front north of the state will weaken
the high far northeast of Hawaii and slide it southward on Friday.
Winds will strengthen slightly and back to a more easterly
direction Friday into the weekend as the high builds south and the
front weakens. Clouds and showers will continue to track over the
islands and focus over windward and mauka areas, with most of the
rainfall occurring over the nighttime hours. Rainfall amounts
should generally be light.

Winds will weaken Sunday and Memorial Day to gentle to moderate in
strength, but remain east. The weakened front will lift northeastward
on Tuesday and further weaken the high pressure system to our
northeast. Winds will weaken and again shift to the east southeast
Tuesday and Wednesday, likely resulting in another round of
daytime sea breezes and nighttime land breezes.


&&

.AVIATION...
The band of showery low clouds that affected windward and southeast
facing areas of Maui and the Big Island this morning has dissipated,
so AIRMET Sierra for mountain obscuration was cancelled. TAF sites
remain mostly VFR and should remain so through tonight. However, models
continue to indicate another band of clouds and showers moving through
tonight, likely impacting the same areas of Maui and the Big Island.
AIRMET Sierra for mountain obscuration will likely be needed again later
tonight through Friday morning for those areas, before dissipating.

Winds are forecast to increase slightly and shift more out of the east
on Friday, so clouds and any showers will likely favor the typical
windward coasts and slopes with less cloud cover over leeward areas
in the afternoon. The Kona coast of the Big Island will remain wind-
sheltered, however, so afternoon clouds are expected there once
again.


&&

.MARINE...
A surface ridge roughly 250 nm north of Kauai will drift
southward over the next couple of days as a front, now sitting
about 400 nm northwest of Kauai, stalls on the edge of the
offshore waters. As a result, easterly trade winds around the Big
Island and Maui County will blow at fresh to low-end strong
levels, putting those waters under border line Small Craft
Advisory (SCA) conditions. Due to the proximity of the front and
blocking from the upstream islands, winds shift out of the east-
southeast and weaken near Oahu and Kauai. As the front dissipates
later Friday and Saturday, the ridge north of the islands will
exert a greater influence, and easterly trade winds will surge
back across the entire island chain. Expect moderate to fresh
trades to then dominate across most waters into next week, with
periods of SCA conditions possible for the typically windy waters
around the Big Island and Maui.

Near to above seasonable average surf is due along south facing
shores through the holiday weekend, while north facing shores see
a brief pulse above seasonable average. The current south-
southwest swell will produce surf mainly in the head high range
through Friday. As this swell declines on Saturday, forerunners
from a larger south-southwest swell will fill in, and south shore
surf will peak around the 8 foot advisory level on Sunday and
Memorial Day. Surf will drop to near seasonable average during
the middle of next week. A pulse of relatively short period
northwest swell will arrive late Friday and peak Saturday and
early Sunday, producing surf a few feet over seasonable average
though well below the north shore advisory level. This swell
should drop a notch on Memorial Day, with surf holding around
seasonable average through the middle of next week. Along east
facing shores, trade wind swell will pick up to around seasonable
average (6 ft 8 seconds) late Friday or Saturday, hold through
Sunday, then drop slightly next week.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...Foster
AVIATION...TS
MARINE...Wroe

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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