Area forecast discussion
National Weather Service Honolulu HI
330 am HST Wednesday Jun 19 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 1026 mb high near 33n142w...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 cloud cover across local waters has increased
since last evening...with broken to overcast low clouds embedded
within trade flow across windward waters and large broken low cloud
patches noted across leeward waters. These clouds also cover
windward and Mauka sections of the islands. Return flow keeps thick
cloud cover across leeward and Kau sections of The Big Island this
morning even without the assistance of daytime heating. Sky grids
have been changed changed to account for this increased cloud cover.
Radar shows isolated to scattered light showers...with almost all of
this activity taking place over water. Latest soundings show a
strong inversion at around 7800 feet...capping the depth of
convection and keeping total rainfall light. Water vapor loop shows
broad upper troughing west of the islands...with an area of
scattered to broken high clouds just southeast through 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 later today 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 tonight through Thursday night. The ridge will
rebuild by the weekend and trades will likely become locally breezy
again.
&&
Aviation...
expect little significant change in aviation weather around the main
Hawaiian islands today. Conditions will remain mostly VFR...except
for brief periods of MVFR ceilings and/or visibilities over some
windward and Mauka areas in low clouds and rain showers.
Data from the VAD wind profiles appear to be showing values less
than the threshold which might indicate tempo moderate low-level
mechanical turbulence may occur leeward of the mountains on the
islands. Therefore...we do not anticipate issuing an airmet for
low-level turbulence this morning.
&&
Marine...
a Small Craft Advisory...sca...is in effect through this afternoon
for locally strong trade winds and rough seas in the windier areas
around Maui and The Big Island. Winds will subside slightly tonight
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 today for Maalaea Bay...the
waters south of The Big Island...and the pailolo and alenuihaha
channels.
&&
$$
Public/marine...Powell
aviation...Houston
