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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 131313 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
313 AM HST Mon Jul 13 2020

A high pressure system north of the islands will keep moderate to
locally breezy trade winds in the forecast for one more day. An
upper level disturbance will line up with a low level trough
passing from east to west across the state. Expect an increase in
shower activity trends today as both system move across the
state. Trade winds will decrease in strength starting on Tuesday
as the high pressure center drifts further north away from the
Hawaiian Islands. These lighter trades will allow light sea
breezes to develop over sheltered leeward areas each day with
light winds lasting through the end of the week. Stronger trade
winds are forecast to return just in time for the weekend.


Corrected Aviation Section.

Satellite imagery this morning shows a similar pattern with an
upper level low roughly 600 miles north of the Big Island drifting
slowly westward along a narrow upper level trough. The
subtropical jet stream continues to produce high clouds over the
state today. A low level trough is moving through the eastern
islands and shows up on satellite as unstable cumulus cloud bands.
Local radar imagery shows numerous showers moving into windward
areas with more scattered shower coverage for leeward locations.

This upper level low will produce large scale atmospheric lifting
across the state. Meanwhile at the 700 mb level a lower level
trough will produce low level convergence. These two disturbances
will combine forces today producing periods of enhanced shower
activity statewide. Moderate to locally breezy trade winds will
focus the highest shower coverage over windward and mountain
slopes, however the larger scale instability will allow scattered
showers to drift into leeward areas.

In the big picture, a high pressure system north of the Hawaiian
Islands will keep moderate to locally breezy trade winds in place
today. By Tuesday, this high pressure system drifts northeast
away from the islands, decreasing local wind speeds, and allowing
thermally driven land/sea breezes to develop over leeward areas.
This light easterly wind pattern will continue through Friday.
High pressure builds back in by Saturday with another increase in
showers just in time for the weekend.


An elongated ridge of high pressure north of the state will
maintain moderate to occasionally breezy trades across the islands
this morning and into early afternoon. Scattered to numerous
showers will mainly affect windward locations and bring periods
of MVFR conditions due to lowered ceilings and visibility.

AIRMET SIERRA remains in effect above 2500 feet for north through
east sections of Oahu, Molokai, and Maui due to tempo mountain
obscuration from clouds and showers.

AIRMET TANGO remains in effect below 8000 feet for south thru
west of mountains on all islands due to tempo moderate turbulence.


High pressure north-northeast of the islands will keep fresh to
strong trades in place today. As a result, a Small Craft Advisory
(SCA) remains posted for the typically windy waters around Maui
County and the Big Island. A couple troughs of low pressure will
pass by to the north of the state Tuesday through Friday, easing
the trades into the light to moderate range in most areas, with
fresh trades periodically affecting the typically windier channel
waters. Trades should then ramp back up to locally strong levels
next weekend as high pressure strengthens far to the north of the
island chain.

There will be a series of small southerly swells over the next
several days that will keep south shore surf near of just above
background levels. A slightly larger long period south swell may
fill in Friday and Saturday. East facing shores will continue to
experience short period choppy surf produced by the trade winds. A
small but slightly longer period east swell produced from
former tropical cyclone Cristina, may provide a slight uptick in
surf heights during the late Tuesday through Thursday time
frame. No other significant swells are expected.


Small Craft Advisory until 6 PM HST this evening 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

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