Area forecast discussion
National Weather Service Honolulu HI
830 PM HST Tuesday Jun 18 2013
Synopsis...
expect trade wind weather to continue through the forecast
period...thanks to persistent high pressure to our north. Clouds and
showers will favor windward and Mauka areas...mainly at night and
during the morning hours. Leeward areas of The Big Island will see
increased clouds and showers each afternoon and evening.
&&
Discussion...
a 1028 mb high near 33n144w...far northeast of the main Hawaiian
islands...has an associated ridge which extends west through
30n170w. This ridge is about 600 miles north of the main Hawaiian
islands and easterly trade winds dominate across local waters.
Satellite loop shows patchy broken low clouds embedded within trade
flow across windward waters. These clouds also cover windward and
Mauka sections of the islands. Return flow and afternoon heating
keep thick cloud cover across leeward and Kau sections of The Big
Island this evening. However...unlike windward cloud cover...we
expect leeward Big Island cloud cover will decrease overnight. Radar
shows isolated to scattered light showers. Afternoon soundings show
a strong inversion at around 7200 feet...capping the depth of
convection and keeping showers fairly light. Water vapor loop shows
broad upper troughing west of the islands...with an area of broken
high clouds just east of the islands marking its eastern flank.
Models show the atmosphere becoming drier...with low-level moisture
getting shallower over the next 24 hours. Rainfall will likely
become quite sparse Wednesday through Friday. With trade winds
continuing...this sparse rainfall will be concentrated over windward
areas. Models also continue to show a big low developing near the
Aleutians over the next couple of days...with the subtropical ridge
to its south weakening and shifting southward. That should weaken
the pressure gradient over the islands and cause trade wind speeds
to drop off a bit Wednesday night through Thursday night. The ridge
will rebuild by the weekend and trades will likely become locally
breezy again.
&&
Aviation...
there should be little change in aviation weather around the main
Hawaiian islands through early Wednesday morning. Conditions will
remain mostly VFR...except for brief periods of MVFR ceilings over
some windward and Mauka areas.
&&
Marine...
a Small Craft Advisory...sca...is in effect through Wednesday
afternoon for locally strong trade winds and rough seas in the
windier areas around Maui and The Big Island. Winds will subside
slightly Wednesday night through Thursday night...probably enough to
allow US to drop the Small Craft Advisory for a day or two. A Small Craft Advisory is likely to go
back up again Friday.
Surf will be generally small except for moderate surf along east
shores due to the trade winds. A small southeast swell may affect
The Big Island starting Sunday...but The Big Island will likely
block most of the swell from reaching the rest of the islands.
&&
Hfo watches/warnings/advisories...
Small Craft Advisory until 600 PM HST Wednesday for Maalaea Bay...
the waters south of The Big Island...and the pailolo and alenuihaha
channels.
&&
$$
Public/marine...Powell
aviation...Houston
