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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 150322 AAA

Area Forecast Discussion...UPDATED
National Weather Service Honolulu HI
522 PM HST Tue Jul 14 2020

Late afternoon satellite and radar images indicate showery low
clouds increasing in coverage over waters north of Oahu/east of
Kauai, with these showers poised to soak Kauai through most of the
night. Forecast PoPs were increased to account for this trend.


Light to moderate trade winds will become even lighter from Thursday
into Saturday, with winds strengthening again by Sunday. Decreased
moisture will support fewer windward showers later tonight into
Thursday, but other moisture sources are expected to bring increased
windward showers Thursday night and Friday, and possibly again on
Sunday. Some afternoon clouds and showers can be expected over
leeward areas of the smaller islands when winds are light.


Light to moderate trade winds through Wednesday will become even
lighter from Thursday to Saturday as a trough (remnants of what was
once TS Cristina) passes between the islands and the trade wind
supporting high centered to the distant NE. While a low aloft will
linger NW of the islands and deliver periods of variable high clouds
the next couple of days, a mid-level ridge will build over the area
from the NE, and the island atmosphere will become increasingly
stable. Combined with diminished upstream moisture, fewer showers
are expected through Thursday.

Although the mid-level ridge will remain in place through the
weekend, models are now indicating that some of the moisture pooled
S of the Cristina remnant will move over the islands, bringing an
increase in showers later Thursday into Friday. Afternoon sea
breezes will also drive cloud and shower formation over leeward
areas that will gradually diminish after sunset - daily on the Big
Island, and Thursday-Saturday on the smaller islands when large
scale winds are lightest. Later Saturday into Sunday the trough will
dissipate and the high to the distant NE will strengthen, supporting
a breezy trade wind flow. Models also indicate a surge of moisture
moving across the islands as trades build on Sunday.


High pressure is still centered well to the northeast of Hawaii and
continues to bring the state east to northeast tradewind flow.
Lingering moisture and an upper level disturbance passing over the
western part of the state are keeping the ceiling low for Kauai. The
rest of the state has cleared out nicely and lifted ceilings above
mountain obscuration thresholds for most areas.

AIRMET SIERRA remains in effect for north thru east sections of
Kauai above 2,500ft feet due to tempo mountain obscuration from
clouds and showers.


High pressure far northeast of the state will maintain moderate to
locally fresh trades through Thursday. A weak disturbance is
expected to move to the northeast of the islands Thursday and
Friday, which will likely decrease the trades to light to moderate
speeds Thursday and Friday. Winds may become light enough for
afternoon sea breezes over select leeward waters Thursday and Friday
afternoons. Expect the trades to ramp back up over the weekend as
that disturbance dissipates and the high pressure strengthens to the
north of the state.

Overall, no significant swells are expected through the forecast
period. Small background surf will continue along south facing
shores over the next several days. A small south-southwest swell is
possible over the weekend. East facing shores will continue to
experience small to moderate short period surf produced by the trade
winds locally and upstream of the state. An increase is expected
over the weekend as the breezy trade winds return. Surf along north
facing shores will remain nearly flat through the period.






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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