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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 100155
Area Forecast Discussion
National Weather Service Honolulu HI
355 PM HST Sun Aug 9 2020
A ridge of high pressure north of the islands will maintain
locally strong trade winds through this evening with a gradual
decrease expected during the first half of the week. Passing
showers will be most common over windward and mountain areas,
especially during the overnight and morning hours.
A 1035 mb high located far north of the state will produce strong
trades through this evening. Trade winds are expected to
gradually decrease beginning later tonight and lower to moderate
speeds (10 to 20 mph) by Wednesday. Moderate trade winds are then
expected to hold through Friday with a slight increase possible
Latest radar and satellite imagery are showing some moisture
lingering over the eastern half of the state, while the western
half remains mostly sunny this afternoon. As we head into tonight,
some of the moisture will ride in with the trades and spread to
Oahu and Kauai. Most of the showers will remain light and will
continue to do so through rest of the week. Overall, we will
continue to see our typical trade wind showers through rest of the
week, where showers will be focused over windward and mauka areas
especially during the night time and early morning hours.
Fresh to locally strong trades will support scattered showers with
periods of low ceilings particularly over windward coasts and
slopes. Mountain obscuration lingers over windward Maui and Big
Island due to a band of showery low clouds, so AIRMET Sierra
remains in effect above 2000 for those areas, but can likely be
dropped for this evening as the showers continue to diminish. The
band of low clouds and showers have lessened enough over the
western half of the state to warrant removal from the AIRMET.
Slightly drier trades are forecast to work into the area tonight.
AIRMET TANGO remains in effect below 7000 feet over and south
thru west of mountains for tempo moderate turbulence.
Trade wind speeds have weakened slightly off their peak last
night, but fresh to strong trade winds will continue through
Monday. The Small Craft Advisory coverage area has been trimmed
back to include the windy zones around Maui County and Big Island,
plus the Kaiwi Channel, leeward Oahu and windward Maui County
waters. Winds speeds are expected to continue weakening through
midweek, then maintain moderate to fresh breezes during the second
half of the week.
Surf along east facing shores will remain rough through Monday due
to the gusty trades. Although the surf will lower by midweek as
the winds relax locally, an upward trend is possible through the
second half of the week. Guidance depicts a decent sized area of
strong winds focused at the islands within the 040-050 degree band
off the California coast now through Tuesday, which should
correspond to a medium period groundswell out of the northeast
arriving around Thursday.
Surf along south facing shores will remain small through the
week with mainly a mix of small, short-period southeast and
background south-southwest energy moving through. Small,
background swell is expected over the next day and again at the
end of the week for north facing shores.
Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Small Craft Advisory until 6 AM HST Monday for Oahu Leeward
Waters-Kaiwi Channel-Maui County Windward Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office