High Surf in Hawaii, January 24 to 28, 2021

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
438 PM HST Sun Jan 24 2021

.SYNOPSIS...
Strong high pressure northeast of the area will maintain locally
strong trade winds over the islands through most of the week.
Windward areas will remain rather rainy especially during the
first half of the week. Rainfall will begin to increase over the
Big Island tonight and become more widespread across the state by
Monday night. Drier trades are expected during the second half of
the week.

&&

.DISCUSSION...
A strong high far northeast will produce strong trades (15-30
mph) throughout the week. Winds may drop a notch towards next
weekend, but trade winds should still remain breezy.

Starting tonight, a trough west of the state will slowly move
closer and then lift north of the state. This will cause the
winds to shift toward the southeast and will allow moisture to
move in from the south. The greatest moisture is expected over
the Big Island and a Flash Flood Watch is in effect for the Big
Island starting tonight and continuing through Tuesday. During
this time, east and southeast slopes of the Big Island are
expected to see a prolonged period of moderate to locally heavy
rain showers.

With the abundant moisture moving in over the Big Island, the
peaks of Mauna Kea and Mauna Loa should see a mix of snow showers
and freezing rain. A Winter Weather Advisory is in effect for the
summits starting tonight through Tuesday.

For rest of the state, we should see moisture spread westward by
Monday afternoon. Due to the low level flow mainly being out of
the southeast, there will be some rain shadowing from the Big
Island and areas across Maui County and Oahu should see less
showers compared to the Big Island. On Kauai they will be closer
to the moisture source, which could lead to some locally heavy
showers especially on Tuesday. With strong east to east-southeast
winds expected during this time, the favored areas of
precipitation will be over windward and mountain areas.

During the second half of the week, models are showing the
moisture shifting west of the state and we should see our typical
trade wind weather return. Trade winds will still be on the
strong side though, with 15 to 30 mph trades expected through
most of this week.

&&

.AVIATION...
High pressure northeast of the state will allow for breezy east
southeast flow to continue across the islands this evening.
Relatively deep moisture lifting towards the area from the south
will act to increase cloud cover and showers as the night
progresses, especially along windward portions of the Big Island
and Kauai. MVFR conditions for ceilings and visibility will
likely accompany this activity. Scattered showers expected
elsewhere along windward portions of all other islands and
isolated showers leeward.

AIRMET TANGO remains in effect over and immediately west of
mountains on all islands due to tempo moderate turbulence.

&&

.MARINE...
Strong east-southeast winds associated with high pressure to the
NE and low pressure to the WNW will continue through the upcoming
week. A Small Craft Advisory is in place across the coastal
waters for winds and seas. Surf along east facing shores will
remain elevated through midweek and a High Surf Advisory is in
place.

Surf along north and west facing shores will steadily lower
through Monday as a NW swell eases. A large scale weather change
across the Pacific will translate to smaller surf for north and
west facing shores Monday through Thursday. For the long range,
wave models show a smaller long period swell arriving in Hawaii
Thursday out of the WNW, then trending up from the NW Friday and
Friday night. However, large errors typically associated with
these sources lead to low forecast confidence.

Surf along south facing shores will trend up late Monday into
Tuesday and hold through midweek as a long period, SSW swell
arrives.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Tuesday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.

Flash Flood Watch from 6 PM HST this evening through Tuesday
afternoon for Big Island.

Winter Weather Advisory from 6 PM this evening to 6 PM HST
Tuesday for Big Island Summits.

Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian
waters-

&&

DISCUSSION...Kino
AVIATION...Thomas
MARINE...Morrison