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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 210123
Area Forecast Discussion
National Weather Service Honolulu HI
323 PM HST Fri May 20 2022
Building trades will become locally breezy this weekend and bring
a return to normal humidity levels and a typical distribution of
clouds and showers focused over windward areas.
A deep, moist airmass remains entrenched over the western half of
the state where CIMSS PWAT analysis indicates PWATs near or in
excess of 2 inches from Molokai to Kauai. While locally heavy
showers have been observed at times through the day, a greater
coverage of heavy showers has been limited by the abundance of
low and mid-level clouds stagnating over Oahu and Kauai.
Meanwhile, thunderstorms over upslope portions of interior Big
Island will diminish with the loss of heating this evening.
As broad mid-level ridging strengthens to 593dm at 500mb off the
southern California coast during the weekend, high pressure will
establish upstream resulting in a gradual return to typical trade
wind weather. An ESE flavor of trades continues over the eastern end
of the state continues through tonight, turning increasingly easterly
and locally breezy during the latter half of the weekend. Returning
trades will usher the humid airmass westward which will begin taking
the edge off the humidity over Oahu on Saturday and Kauai by Sunday.
In the meantime, the lingering moist airmass may support another
round of interior showers over portions of Kauai on Saturday
afternoon. Locally breezy, and stable trades return Sunday and
continue into next week.
A nearly stationary remnant frontal boundary lies over the west
end of the island chain. Clouds and showers associated with this
boundary is producing occasional MVFR conditions with isolated IFR
conditions occurring in a few moderate to heavy showers as well.
Daytime heating has also allowed for isolated thunderstorms to
form over the slopes of Mauna Loa. Expect shower activity to
diminish overall across the area overnight. No AIRMET's are
currently in effect but lingering moisture around Kauai and Oahu
may cause the issuance of one. A drier and more stable airmass
will begin to fill in from the east later tonight and early
A stalled front near Kauai will continue to weaken and drift
northward. High pressure will start to build into the region
tonight and Saturday, with easterly trade winds strengthening
from east to west through the weekend. SCA conditions will likely
return to the typical windier waters and channels around Maui
County and the Big Island Saturday night. Typical trade wind
weather with more stable conditions will continue into the middle
of next week.
Surf heights along south facing shores will remain elevated into
next week, as the current south swell becomes reinforced by
additional long-period south swells arriving on Saturday, Monday
and next Thursday, fluctuating slightly between swells. In the
long range, models continue to show quite a bit of activity in the
southern hemisphere, which could translate to additional south
shore surf events lasting into early June.
Surf along north and west facing shores will slowly decline as
medium-period northwest (300-320 degrees) swell energy diminishes
over the next couple of days. A return to nearly flat summer
conditions is expected Sunday through the first half of next week.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office