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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 250134

Area Forecast Discussion
National Weather Service Honolulu HI
334 PM HST Sat Oct 24 2020

The wet pattern over the western end of the state will linger
through much of next week as a front and upper disturbance
approach and move into the area Sunday through Wednesday.
Moisture moving in from the east will support increased shower
coverage across Maui County and the Big Island through the
weekend. A more widespread rainfall event will be possible next


Satellite loop shows a frontal boundary about 520 miles northwest
of Kauai, supported by deep troughing aloft. A smaller weak upper
trough just north of the islands is lifting to the north this
afternoon, allowing generally drier and more stable conditions to
build in from the east. While this has translated to less shower
coverage across the area compared to the past several days, spotty
showers will remain in the forecast due to a persistent plume of
low level moisture and light to moderate south to southeast low-
level flow. The best chance for showers will remain over mauka
areas Sunday afternoon as sea breezes develop. Additionally, a
patchy cloud band drifting in from the east will support a slight
increase in shower coverage over Maui County and the Big Island
through the rest of this weekend.

Models show the upper trough northwest of Kauai will dig
southeastward toward the region, driving the front into the area
beginning Tuesday. The resulting wet and humid conditions will
then persist through the week as the front and upper trough
linger. Increased moisture and instability may also support
thunderstorm development. Given the amount of recent rainfall, the
potential for additional heavy rainfall next week may increase
the risk for flash flooding, especially over Kauai and Oahu. A
Flash Flood Watch may be issued for these areas sometime over the
next day or two as this situation develops.


Visible satellite and radar show the bulk of the shower activity
around Kauai this afternoon. The band of moisture that affected
the Big Island this morning has diminished, but spread westward
to the Maui County windward waters. Light convergent flow out of
the south to southeast will continue through the forecast period
bringing periods of showers and MVFR conditions, especially
during the afternoon/evening as sea breezes become established.
Land breezes will clear out most leeward areas overnight. Slightly
stronger east-southeast flow is expected Sunday afternoon for
windward areas as far west as Oahu, while leeward areas experience
sea breeze development once again.

No AIRMETs are currently in effect nor expected through Sunday.


Strong high pressure northeast of the state and a trough of low
pressure to the northwest will keep moderate to fresh southeast
winds over the eastern islands, and light and variable winds over
the western end of the state through the weekend. An approaching
front is expected to increase southerly winds, heavy rainfall,
and thunderstorms next week.

The highly anticipated long- period northwest swell has arrived
at Buoy 51001 and is expected to reach Kauai and Oahu tonight.
Surf will approach advisory levels along north and west facing
shores of Kauai and Oahu by tomorrow morning. Surf will gradually
lower through the middle of next week.

Surf along south facing shores will remain small with a mix of
long-period south and short-period southeast swells through next
week. Surf along east facing shores will remain small through the
weekend with a bump in surf expected Monday and Tuesday.






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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