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RH39 %
WindSSW 6 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 241332

Area Forecast Discussion
National Weather Service Honolulu HI
332 AM HST Sat Oct 24 2020

The persistent wet and humid pattern in place over the western
end of the state is expected to linger through much of next week
as another cold front and upper disturbance approach and move
into the area later this weekend through next Wednesday. A modest
increase in moisture moving in from the east will support better
shower coverage for Maui County and the Big Island over the
weekend. A more widespread rainfall event will be possible next
week, which will translate to an increasing concern for flash
flooding given the recent heavy rainfall on Kauai and Oahu.


Water vapor imagery depicted an amplified upper pattern over the
northern Pacific with persistent upper troughing north to northwest
of Hawaii. The upper low positioned nearby to the north is
opening up and beginning to lift off to the north and away from
the area. Some drier middle- to upper-level air and rising upper
heights will be anticipated briefly as this feature pulls away
from the area today through Sunday. Although this will translate
to more of a stable environment compared to the past several days,
spotty showers will remain in forecast due to the persistent
plume of moisture and light southerly low-level flow in place.
The best chances for showers will remain over Kauai and Oahu
through the afternoon hours as sea breezes develop. A modest
increase in moisture, however, filling in from the east will
support a slight increase in shower coverage over Maui County and
the Big Island this weekend where very little rainfall has

Guidance has initialized well with the current pattern and shows
the progressive pattern continuing early next week as a potent
shortwave trough digs southeastward toward the region driving
another cold front into the area Tuesday through midweek. This
will result in the wet and humid conditions persisting. Given the
recent periods of heavy rainfall and moistening soils, the main
concern with this scenario will be the threat for heavy rainfall
and flash flooding - especially over Kauai and Oahu. In addition
to the rainfall potential, increasing instability and lift will
support a few thunderstorms. Confidence in the details will follow
in later packages this weekend as this scenario unfolds.


Light convergent flow out of the southerly quadrant will continue
through the forecast period bringing periods of showers and MVFR
to leeward areas, especially during mid to late day Saturday once
sea breezes become established. A band of deeper moisture
immediately east of the state per regional satellite imagery will
work westward this morning resulting greater inland shower
coverage for Molokai through Big Island compared to recent days.

No AIRMETs in effect.


Strong high pressure northeast of the state and a trough of low
pressure to the northwest, will keep a fairly stagnant pattern
in place across the marine area through the weekend. Moderate to
fresh southeast winds will prevail over the eastern islands,
while winds remain light and variable over the western end of the
state. An approaching front may bring increasing southerly winds,
heavy rainfall, and thunderstorms to much of the area by the
middle of next week.

Surf along north and west facing shores will remain very small
though this morning, then gradually increase late this afternoon
as a long-period northwest swell arrives. This swell will fill in
tonight, with surf possibly approaching advisory levels along
north and west facing shores of Kauai and Oahu as it peaks on
Sunday. North shore surf will then gradually lower through the
middle of next week, then hold at small levels heading into next

Surf along south facing shores will remain small with a mix of
long-period south and short-period southeast swells moving

Surf along east facing shores will remain small through the
weekend, then trend up early next week as a small northeast swell






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