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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 270159
Area Forecast Discussion
National Weather Service Honolulu HI
359 PM HST Thu Nov 26 2020
Trade winds will focus clouds and showers over windward and mauka
areas through the weekend. Shortwave energy could destabilize the
weather over the eastern islands and waters this weekend. Winds
will taper off during the first half of next week as a cold front
approaches. The front will dissipate on Wednesday before it
reaches the islands.
High pressure systems northeast and northwest of Hawaii are driving
fresh trade winds across the island chain this afternoon. Aloft, a
weak upper trough over the eastern end of the state moving to the
east while more stable northwesterly flow fills in behind. 00Z
soundings at Hilo and Lihue show that a weak inversion has
developed over the state and precipitable water values have fallen
back to a near-normal 1.4 inches. Visible satellite and radar show
scattered clouds and showers focused on windward sides of Kauai,
Oahu on the Kona slopes of the Big Island. Mostly sunny to partly
cloudy skies prevail across the the remaining leeward sides.
The upper trough will linger east of the area through the weekend,
while upper level ridging will nose in from the west, placing the
islands under a somewhat stable northwest flow. Two shortwave
energy pulses will quickly move through the upper trough, first on
Friday night and again on Sunday night/Monday before the upper
ridge definitively takes over next week. These pulses could
trigger a few heavy showers or thunderstorms near Maui and the Big
Island. Most likely scenario is the heavy rain/thunderstorms
stays just east of both islands, but can't completely rule out an
impact to either island.
At the low levels, moderate to fresh trades will continue to
direct clouds and showers over windward and mauka sections through
the weekend. A few showers will likely spill over to leeward
sides of the smaller islands at times due to the strength of the
winds. Trades will back more northeasterly Friday into Sunday as a
surface trough sets up northeast of the area (that will not
directly affect us).
Next week, winds will taper off as a cold front approaches from
the northwest. Daytime sea breezes/nighttime land breezes may be
possible on Monday. The front will dissipate north of the area on
Wednesday, with trade winds the front and reaching the islands
by Tuesday. Another front will approach the state next weekend.
High pressure far northeast of the area will shift eastward and
be replaced by a new high building in to the north of the state
tonight and Friday. This will keep a moderate to locally breezy
trade wind flow in place through Friday. Clouds and passing
showers will favor windward and mauka areas with a few brief
showers falling over select leeward areas at times.
AIRMET Tango remains in effect for moderate low level turbulence
downwind of terrain on all islands due to the moderate to breezy
trade winds. This AIRMET will continue through the overnight
hours. A sharp eastward moving upper level trough is causing
moderate upper level turbulence from Oahu eastward to the Big
Island. As the trough shifts slowly eastward, conditions should
improve over Oahu and possibly parts of Maui County overnight and
With high pressure persisting far north of the area, trade winds
will continue to be moderate to locally breezy across the coastal
waters over the next several days. A Small Craft Advisory remains
posted for the typically windy zones around Maui County and the
Big Island through early Friday morning, and may need to be
extended beyond that time period.
A series of northwest and/or north-northwest swells will affect
the local waters and coasts through next week. The latest model
runs indicate a large, long-period northwest to north-northwest
swell may begin arriving late Monday or early Tuesday. If this one
materializes, it will bring High Surf Advisory, even Warning,
conditions to north- and west-facing shores.
Surf along east-facing shores will remain somewhat elevated
through the weekend as trade winds persist. Surf along south-
facing shores will be small into next week.
Small Craft Advisory until 6 AM HST Friday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office