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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 030642

Area Forecast Discussion
National Weather Service Honolulu HI
842 PM HST Tue Mar 2 2021

Breezy to windy trades will persist tonight, then slowly decrease
during the next few days. Fairly typical trade wind weather will
persist through Thursday, with showers favoring windward and mauka
areas, particularly at night and into the early morning hours. A
surface trough will develop in the vicinity of the islands
Thursday night, then slowly shift westward Friday and Friday
night. This will bring wet trade wind conditions particularly to
windward sections of the smaller islands. As the trough shifts
westward, a more typical but slightly wetter than normal trade
wind pattern will return over the weekend, with trades increasing
back to breezy levels. The trades will strengthen further to
windy levels early next week, with the wetter than normal trade
wind conditions persisting.


Currently at the surface, a 1043 mb high is centered around 1700
miles northwest of Honolulu, and is driving breezy to windy
easterly trades across the island chain this evening. Infrared
satellite imagery shows mostly cloudy conditions in most windward
areas, and partly cloudy skies in most leeward communities.
Additionally, a roughly 50 mile wide band of enhanced cloud cover
is seen around 40 miles to the east-northeast of the islands this
evening. Radar imagery shows scattered to numerous showers moving
into windward areas, with the trades blowing a few showers into
leeward sections from time to time. Further upstream, some
enhanced showers are seen in association with the cloud band
mentioned above moving into the nearshore coastal waters. Main
short term concerns revolve around trade wind trends during the
next couple days.

High pressure northwest of the islands will gradually weaken as it
settles southeastward during the next few days. Breezy to locally
windy trades will continue tonight, ease to breezy levels
Wednesday, then diminish to moderate speeds Thursday through
Friday. Latest observations indicate than winds have dropped below
advisory levels, and with the downward trend expected overnight,
will go ahead and cancel Wind Advisory with the evening forecast
package. A weak surface trough will develop in the vicinity of
the islands on Friday, then shift westward Friday night as a new
strong 1040+ mb high builds north of the state. This strong high
will slowly settle southeastward through early next week, with
breezy conditions expected over the weekend, and windy conditions
developing for the first half of the new week.

As for the remaining weather details, fairly typical trade wind
weather will prevail through Thursday, with showers favoring
windward and mauka areas, particularly at night and through the
early morning hours. A cloud band upstream of the islands will
increase shower coverage as it passes through the islands later
tonight. We should see things dry out nicely by mid morning
Wednesday, with only a few showers expected through the remainder
of the day, mainly in windward areas. Another band of clouds and
showers which can be seen in satellite imagery further upstream to
the northeast of the state this evening, appears on track to move
through the islands Wednesday night bringing another increase in
shower coverage. Expect conditions to dry out similarly on
Thursday, although quite a bit of high cloud cover will be
overspreading the islands as an upper level trough digs to the
northwest of the state.

A weak surface trough will develop in the vicinity of the islands
Thursday night along the tail end of an old front. This surface
trough will then slide slowly westward Friday and Friday night.
Moisture from the surface trough combined with added instability
from the trough aloft will lead to an increase in shower coverage
and intensity across the islands during this time, with the
potential for some locally heavy rainfall over windward areas. At
the moment, the deepest moisture appears to target the smaller
islands, particularly Kauai and Oahu. Once the surface trough
shifts west of the state, we should see a fairly typical but
slightly wetter trade wind pattern develop for the weekend, which
will continue into early next week.


A surface high to the northwest of the state will continue to
support breezy to locally strong easterly trade winds throughout
the night and into tomorrow, though speeds should gradually
diminish throughout the period. Latest satellite imagery and
model data depict a band of moisture approaching the islands from
the east this evening. This will pass over the state tonight and
favor showers with periods of MVFR level clouds for north through
east sections of the islands through the early morning hours.

AIRMET Tango remains in effect for moderate to severe low-level
turbulence near and downwind of the terrain given the locally
strong surface winds. It also accounts for moderate mid-level
turbulence between FL220 and FL300. Wind speeds are expected to
not be quite as strong in the vicinity of Maui and the Big Island
tomorrow, so it is possible that the AIRMET Tango for surface
winds greater than 30kts may be cancelled during the early morning


A Gale Warning remains in effect for the Alenuihaha channel and
for waters lee and south of the Big Island through tonight. A
Small Craft Advisory (SCA) remains posted for the remaining
waters due to a combination of strong trade winds and elevated
seas. The Gale Warning will be downgraded to an SCA and include
all other waters early tomorrow morning through tomorrow
afternoon. The SCA may be scaled back briefly to typically windy
waters around Big Island and Maui County tomorrow night. Building
high pressure to the northwest of the state will boost trades
first over waters west of Kauai, then across remaining waters
Thursday into the weekend. This may warrant an expansion and
continuation of the SCA.

Large trade wind-driven seas will maintain east shoreline surf
above the 8 foot High Surf Advisory (HSA) threshold through
tomorrow afternoon. As trade winds over and upstream of the
islands weaken late tonight into tomorrow, surf along eastern
exposures will lower to borderline HSA levels by tomorrow evening,
becoming small by Thursday. Increasing trade wind swell and an
arriving northerly swell at the end of this week and into the
weekend will provide a bump in east shoreline surf.

A northwest swell will begin arriving tomorrow afternoon and
evening, peaking surf along north and west-facing shores late
Thursday into Friday. The secondary north swell will arrive
Friday and, in addition to the returning trade wind swell wrap,
will keep surf at, or slightly above, HSA heights through the end
of this week and into the weekend.

Surf along south-facing shores continues to pull in some trade
wind swell wrap with an expected decline tomorrow with the easing
trades. A southwest swell will fill in late tomorrow through
Thursday before slowly declining through the weekend, which will
keep south shore surf from going flat.


High Surf Advisory until 6 PM HST Wednesday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Small Craft Advisory from 6 AM to 6 PM HST Wednesday for Maalaea
Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-
Big Island Southeast Waters.

Gale Warning until 6 AM HST Wednesday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 PM HST Wednesday for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi
Channel-Maui County Windward Waters-Maui County Leeward Waters-
Big Island Windward Waters.




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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