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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 261949
Area Forecast Discussion
National Weather Service Honolulu HI
949 AM HST Sun Jun 26 2022
Scattered showers are expected over favored leeward
areas today while moderate trades will continue to deliver
relatively limited showers to windward zones through Wednesday.
Locally breezy trades will return as early as Monday afternoon
with an uptick in trade shower coverage likely during the latter
half of the week.
Local visible imagery reveals mostly sunny skies
over the smaller islands and upstream waters early this morning.
Light to moderate trades will continue focusing only very limited
showers over windward zones for the next 24 hours. However, the
emerging hybrid sea breeze pattern late this morning through this
afternoon will allow for renewed convective development over
leeward zones, particularly those in Maui County. While a few
locally heavy showers will be possible, overall shower intensity
in these areas will be markedly lower than yesterday courtesy of
slowly diminishing moisture and slightly increased stability. For
the Big island, lingering clouds associated with overnight
showers, both windward and leeward, are now dissipating in favor
of interior cloud development associated with diurnal heating.
Similar to yesterday, a healthy coverage of interior showers can
be expected, particularly for leeward areas while mostly dry
conditions are likely along the lower slopes of the windward
coast. Enhanced leeward moisture will once again contribute to
shower development along the Kona coast tonight.
Late today into tonight building trades will usher westward what
remains of the existing batch of low-level moisture. Locally breezy
trades are forecast to be in place as early as Monday afternoon with
gradual strengthening then anticipated heading into mid-week. While
stronger trades will more efficiently drive trade wind showers over
windward zones, a much drier mid-level airmass working westward
through the area will provide increased stability even as the
inversion itself potentially remains somewhat weaker and more
elevated. As a result, windward shower coverage is forecast to be on
the drier side through at least Wednesday.
During the latter half of the week, expanding easterly flow through
700mb will eventually be able to tap into the reservoir of greater
moisture presently along/east of about 130W per the CIMSS PWAT
product. By Thursday or Thursday night, weakened stability and
increased moisture evident in model forecast soundings will
contribute to a more typical coverage of trade showers.
VFR conditions prevail at all TAF sites and these conditions are
expected to continue through the day and on into the evening
hours. There may be brief periods of MVFR conditions at windward
terminals such as PHTO in low clouds and SHRA. AIRMET Sierra is
in effect for mountain obscuration across windward sections of
Maui County and the Big Island as an area of moisture embedded in
low level trade wind flow interacts with island terrain. Expect
some improvement in conditions this afternoon.
Trade winds will hold at gentle to moderate speeds through
tonight as a front passes between the islands and a surface high
well north of Kauai. The high will build far northeast of the
state Monday and Tuesday, leading to an increase in trade winds.
A Small Craft Advisory will should be needed for the typically
windy waters around the Big Island and Maui through at least the
middle of the week, and likely through next weekend.
Two pulses of south swell will produce elevated south shore surf
this week. Long period forerunners (17-19 seconds) of the first
swell have been building this morning at the Barbers Point PacIOOS
buoy, and recent trends at the NOAA buoys south of the islands
suggest that the swell may come in larger than expected this
afternoon and tonight, possibly leading to surf near the High Surf
Advisory level of 10 feet into Monday. The next pulse of south
swell is due on Tuesday and Wednesday and could be slightly
larger. This swell will gradually decline Thursday and Friday.
Surf along exposed north and east facing shores could see a bump
in small, short period swell today into Monday, but this swell is
running smaller than expected based on recent buoy readings. Surf
along north shores will drop Tuesday, while strengthening trade
winds will boost rough east shore surf to around seasonal average.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office