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RH9 %
WindE 9 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 090628

Area Forecast Discussion
National Weather Service Honolulu HI
828 PM HST Wed Jul 8 2020

The breezy trade wind pattern will continue through early next
week. Windward shower coverage is expected to increase late
tonight through early Friday as a mid-level disturbance and higher
moisture move through from east to west. Drier trade wind
conditions will prevail Friday through early next week.


Latest surface analysis and satellite imagery showed the subtropical
ridge anchored north of the islands and patchy low-level clouds
approaching and moving through from east to west. Some of these
clouds are generating brief showers as they move through - mainly
over windward and mountain areas this evening. Rain gages around the
islands reflect this and showed peak accumulations ranging from a
quarter to half of an inch over the past 6-Hrs (through 7 pm HST).
Although no significant changes are anticipated for much of the
night, satellite-estimated precipitable water (PW) imagery depicted
a decent sized area of higher moisture approaching from the east
with the leading edge currently a few hundred miles east of Hilo
(values up to around 1.6 to 1.7 inches).

Guidance has initialized well with this upstream moisture and
shows it moving into the eastern end of the island chain late
tonight into Thursday, then to the western end of the state late
Thursday through early Friday. A combination of this moisture, a
mid-level trough moving through and breezy trades will support an
increase in windward shower coverage through this time. Some could
be briefly heavy and make it into leeward areas. Drier air will
follow beginning Friday as this moisture and mid-level feature
shift west of the area.

Although confidence remains very low being this far out in time,
model solutions are trending toward a wet middle- to latter-half
of next week as a remnant trough associated with Tropical Storm
Cristina in the far eastern Pacific approaches and moves into the
area. Additional fine tuning of the forecast will be expected
over the coming days as forecast confidence rises.


Strong high pressure far northeast of the state will continue to
generate moderate to breezy trade wind flow. Surface wind speeds
will decrease overnight, but redevelop Thursday afternoon. Breezy
winds at summit level combined with a well defined inversion aloft
at approximately 09kft are generating low level mechanical
turbulence to the lee of higher terrain. AIRMET Tango will likely
remain necessary through Thursday afternoon and possibly beyond.

Bands of low topped cumulus showers embedded in the trade wind
flow will continue to impact mainly north and east facing slopes
and coasts. Isolated MVFR CIG or VIS are to be expected in
passing showers, otherwise VFR conditions will prevail all areas.

Meanwhile, across Leeward Big Island, light sea breezes will give
way to weak land breezes within the next few hours. Partial
clearing has already begun across Leeward and Interior Big Island,
and mostly clear skies are expected by morning. Both the sea
breezes and the interior cumulus build-ups will redevelop across
leeward and Interior Big Island Thursday afternoon.


Fresh to strong trade winds will prevail through the weekend and
into early next week, as strong high pressure holds in place far
north and northeast of the islands. A Small Craft Advisory (SCA)
remains in effect for the typically windier waters around Maui
and the Big Island through Sunday. This SCA will likely need to be
extended into early next week.

No significant swells are due through much of the week. A mix of
mainly background southerly swells will dominate, with a south-
southwest swell giving south shore surf a bit of a boost Thursday
and Friday. Trade wind swell will gradually build to around the
summer average by Thursday, then hold into early next week. A
small long-period swell from the tropical cyclone Cristina could
arrive early next week as well. Surf along north facing shores
will remain small through the next 7 days.


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




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