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Temp-3.0 C
RH58 %
WindN 13 mph
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Hawaiian Islands Synoptic Discussion and Guidance

213
FXHW60 PHFO 050630
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Sat Feb 4 2023

.SYNOPSIS...
An upper low over the state will maintain an unstable and moist
airmass, which will generate showers and isolated thunderstorms,
with locally heavy rainfall, through the remainder of the
weekend. The upper low will weaken and exit east of the islands by
Monday. Much drier and more stable conditions will filter across
the state to begin the work week, while a more typical trade wind
weather pattern develops across the islands into next weekend.

&&

.DISCUSSION...
Current radar shows showers remaining across the islands this
evening, becoming more focused along windward slopes as locally
breezy trade winds continue across the region. Radar estimates
suggest locally enhanced rainfall rates remaining embedded within
some of the showers this evening. The latest lightning data shows
a few strikes in the vicinity of the Big Island, around 200 miles
north to northeast of Hilo, in an area of enhanced instability
(Showalter Index (SW) around -2c).

Tonight through Sunday...the upper low will remain anchored over
the state tonight, before slowly moving eastward and becoming
centered across the Big Island Sunday night. This pattern will
maintain deep layered moisture (PWs greater than 1.50") and
modest instability (SW around 0 to -1c) across the state through
Sunday afternoon. The deeper moisture and lingering instability
will then become mainly concentrated across the eastern end of the
state Sunday night into early Monday. Thunderstorm probabilities
show the best chance for isolated storms to remain across
windward zones and surrounding waters, and vicinity of the Big
Island through Sunday afternoon. Drier and more stable conditions
will then begin to push in across the western end of the state
Sunday night into early Monday. Overall, will maintain the current
forecast trend, with showers and isolated thunderstorms becoming
mainly focused along windward areas and marine waters through
Sunday afternoon.

Monday and Tuesday...the transition toward more stable and dry
conditions will continue Monday, as the upper low weakens and
exits eastward of the state. High pressure drifting well north of
the region will further strengthen the trade wind weather pattern
across the islands to begin the work week. This pattern will
reinforce the trend toward drier and more stable conditions
across the islands. However, current trends suggest enough
moisture lingering around the islands (modeled PW values 1.25 to
1.35", moisture depths 9k-13k ft) to maintain increased areal
coverage of showers across windward locations into Tuesday.
Showers will remain focused across mainly windward areas. However
the airmass will quickly stabilize through the beginning of the
week, which will greatly reduce the threat of locally heavy
rainfall.

Wednesday into next weekend...the airmass continues to become more
dry and more stable, with forecast PW values falling to under
1.00" while modeled moisture depths fall to around 8k ft or less.
This pattern will greatly reduce the intensity and areal coverage
of showers across the islands. Lingering trade wind flow will
maintain showers to mainly favored windward locations, with the
most persistent showers at night through early morning hours.

&&

.AVIATION...
Breezy easterly trade winds will prevail through the 24-hr
forecast period, with clouds and showers favoring windward areas.
Shower coverage may increase overnight as an area of moisture
continues westward through the area. Some showers will may be
heavy at times and a thunderstorm or two can't be ruled out with
the added instability associated with an upper low over the
islands. With the breezy trades in place, some showers will manage
to reach leeward areas.

AIRMET Sierra for tempo mountain obscuration will be possible
later this evening and through the second half of the overnight
period as the aforementioned area of moisture moves through.

AIRMET Tango for moderate low-level turbulence will continue over
and downwind of island mountains.

&&

.MARINE...
A strong high pressure system passing north of the Hawaii region
will continue to produce fresh to strong trade winds over the
coastal waters through next week. An upper level low over the
eastern islands will continue to slowly drift eastward. This low
will enhance shower activity mainly over southern and eastern
waters on Sunday before drifting away from the region. A Small
Craft Advisory (SCA) remains in effect for all waters due to winds
and seas through tonight. Winds and seas will decrease on Sunday
with stronger trade winds with the SCA decreasing in coverage to
the typical windier waters and channels around the islands in Maui
and Hawaii Counties. More stable conditions are forecast for
Sunday, though a chance for thunderstorms will linger longer over
eastern waters.

A medium period north-northwest to north swell (340-350 degrees)
will hold into Sunday before fading. On Monday, the next long
period northwest swell (310-320 degrees) will arrive and slowly
fill in, peak on Tuesday and Wednesday, and then lower during the
latter half of next week. On Thursday, a larger swell from the
north- northwest (340 degrees) will arrive and may produce surf
near advisory levels for exposed north and west facing shores.
Surf along south facing shores will ease through the weekend as a
long- period south swell energy fades. Surf along east facing
shores will trend up through the early part of the new week as a
belt of fresh to strong easterly trades develops over and far
upstream of the islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Sunday 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.

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


&&

$$


DISCUSSION...SWR
AVIATION...Gibbs
MARINE...Bohlin

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