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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 201400

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Mon Jan 20 2020

Breezy trade winds will continue today, then shift out of the
southeast and diminish Tuesday through Friday. A mostly dry land
and sea breeze pattern will result, with the best chance for a few
clouds and showers setting up over interior areas through the
afternoon periods. A front will stall and weaken near Kauai Friday
with trades briefly returning Saturday.


A broad surface high centered just north of Hawaii will provide
stable conditions and breezy trade winds today. Dew points are in
the low to mid 60s across the state this morning with morning soundings
at Hilo and Lihue indicating a strong inversion around 6 kft and
precipitable water around 1 inch. Infrared satellite and radar
both show an area of concentrated low clouds and showers that
arrived last night and will move across the area, particularly
Oahu and Maui County, through the morning. The low inversion
should keep most of the rain and clouds windward, but may see an
occasional shower reach the leeward side due to the breezy trades.
The clouds and showers should dissipate by this afternoon and any
rainfall will be on the lighter side.

A progressive pattern setting up over the northern Pacific is
expected this week as the polar jet becomes highly zonal. Two
fronts will passing to the north this week, with possibly a third
early next week. The first front will shift the surface high
towards the southeast and bring the associated ridge over the
islands. The winds will respond by veering southeast and
diminishing Tuesday through Friday, allowing a land and sea
breeze regime to setup. Rain chances will remain limited due to
the dry air and strong subsidence expected to continue through
this time period. The best chance for a few clouds and light
showers will shift over interior areas through the afternoon hours
each day.

Long range GFS and ECMWF stall and weaken the second front near
Kauai on Friday, with possible an uptick in showers for the
northern end of the state. Trade winds may briefly return Saturday
as a bubble high quickly passes north of the state before the
next passing front to the north causes the wind to veer out of the
southeast Sunday. This front is expected to weaken as it nears the
island early next week, but it's too early to tell if it will
directly impact the state.


Overnight, stratocumulus reformed near Kauai and Oahu bringing
some lower ceilings to windward areas. More showery low clouds can
be found over the windward areas of Maui and the Big Island, as
well as the adjacent windward coastal waters. The stratocumulus is
expected to burn off by mid morning while some of the showers
will linger over windward areas. Brief periods of MVFR conditions
are possible with these isolated showers, but expect VFR to
prevail overall.

Breezy trade winds warrant the continuation of AIRMET Tango for
tempo low level turbulence below 7,000 feet. Trades will weaken
later today and Tango should be able to be canceled by tonight.


A surface high passing far N of the islands is supporting breezy
to strong NE to E trade winds, and a Small Craft Advisory (SCA)
remains posted for all waters through this afternoon. As the high
moves steadily E and a front approaches from the NW the next
couple of days, winds will veer and gradually weaken as the
associated ridge moves closer to the islands. Winds will become
mainly E today, light SE to variable Tuesday, and light and
variable Wednesday and Thursday as the ridge moves over the
islands. A new high passing N of the islands around Friday will
push a second front toward the islands, while supporting moderate
trade winds heading into next weekend, with the front currently
expected to stall near Kauai and Oahu.

A new long-period NNW swell is expected to peak at low-end
advisory levels today, thus a High Surf Advisory remains in effect
for exposed N and W shores. This swell will diminish late today
and Tuesday, but will be followed on Wednesday by a significantly
larger NW swell that will likely peak near High Surf Warning
heights, with an even larger swell potentially arriving next
Saturday. Choppy surf along E facing shores will gradually
diminish as winds weaken the next couple of days. Winds and seas
have warranted an extension of the existing SCA through this
afternoon, but diminishing winds and seas will allow its
cancellation by tonight or Tuesday at the latest. However, seas
associated with the two large NW swells discussed above will
warrant an SCA for most areas later this week.


High Surf Advisory until 6 PM HST this evening for North and west
facing shores of Kauai, Oahu, Molokai and Niihau, and north
facing shores of Maui.

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




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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