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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 100145

Area Forecast Discussion
National Weather Service Honolulu HI
345 PM HST Thu Jul 9 2020

The breezy trade wind pattern will continue through early next
week. Wetter than normal trade wind weather will continue through
early Friday as a weak disturbance and higher moisture move
through from east to west acoss the state. Drier trade wind
conditions will prevail Friday and Saturday, trending slightly
wetter Sunday into next week.


A 1029 mb surface high is centered 1300 miles to the north
driving fresh trade winds across the state this afternoon. A weak
surface and midlevel trough north and west of the area
(respectively) is currently dragging a broad band of moisture onto
the islands since Wednesday afternoon. 00Z soundings show
precipitable water (PW) values near normal for July at around 1.4
inches. MIMIC satellite Total PW shows a boost to 1.6 moving onto
the Big Island at this hour. Soundings also show a midlevel
inversion present at around 9 to 10 kft. Radar and visible
satellite show broken low cloud cover and scattered showers
focused over the windward slopes. Rainfall amounts have been
light, with locally moderate accumulations in terrain enhanced

Clouds and showers will fill in a bit more tonight as the higher
PW sweeps east to west in combination with the diurnal shower
maximum (at night). Showers will continue to focus windward. Some
showers will periodically make their way to leeward sides of the
smaller islands. Overall, the next 12 to 18 hours should be a
wetter-than-normal trade wind weather pattern for summer.

A large area of stable stratocumulus clouds will move in through
the day Friday, resulting in decreasing showers that will continue
into Saturday. An upper low will set up to the northeast and may
trend the the trade showers up slightly Sunday through Tuesday.
Wind speeds will maintain the current strength into the middle of
next week.

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 and guidance
converges on a solution.


VFR conditions prevail at all TAF sites with brief MVFR
conditions occurring at phto and phny in low clouds. There may be
brief periods of MVFR conditions over windward slopes and summits
of all islands through the evening and on through the overnight
hours as moisture embedded in the trades interacts with island
terrain. There may also be some local MVFR conditions over the
leeward Big Island slopes through the evening hours due to
afternoon cloud buildups.

Airmet TANGO is currently posted over and downwind of mountainous
terrain of Maui County and the Big Island. This will likely be
cancelled later today with an expected drop off in trade wind


High pressure far north and northeast of the state will maintain
fresh to strong trade winds into early next week. Some minor
fluctuations are expected with trades slightly increasing Friday
and Saturday. 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
Monday. Latest model guidance is suggesting a brief decrease of
winds on Tuesday of next week as a weak disturbance passes north
of the state. Winds could briefly drop below SCA thresholds next

No significant swells are due through much of next week. A mix of
background south and southeast swells will continue to produce
small surf along south facing shores through next week. A small
south-southwest filled in during the day today and will likely
hold through Friday morning and taper off in the afternoon. Trade
wind swell will gradually build through Friday, then hold into
early next week. Additionally, a small long-period swell from
tropical cyclone Cristina could arrive early next week. Surf along
north facing shores will remain nearly flat through next week.


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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
Send comments to: Ryan Lyman