Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
830 PM HST Tuesday Aug 26 2014
trade showers continue tonight with rainfall focusing over windward
and mountain areas. The trades will gradually weaken Thursday
through Saturday and allow for sea breezes to develop each day.
This will bring periods of clouds and showers over leeward and
interior areas through the weekend. Then the trades will strengthen
again early next week with showers focusing back over windward and
latest water vapor satellite imagery depicts an upper level low about
570 miles west-northwest of Kauai. The eastern circulation of this low is
pulling some of the scattered layered/high clouds near the inter-tropical convergence zone into
the islands. Meanwhile...surface high pressure remains centered far north-northeast
of the Aloha state and keeping a moderate trade wind regime across
the island chain.
Radar data show showers just east/NE of the islands...bringing periods
of rain over most windward and mountain areas of the smaller
islands...which will continue through the evening and overnight
hours. 00z sounding data and mimic moisture analyses show precipitable waters in
general around 1.15 to 1.30 inches around the main Hawaiian
islands...and a dryer airmass further upstream. Thus...expect
showers with possible localized brief downpours tonight especially
over windward areas...the Koolau Range in Oahu...the west Maui
mountains and windward Haleakala. Then drier conditions will
establish on Wednesday. For the second half of the week...despite the
arrival of a drier airmass...the global models show fair agreement
regarding the passage of the remnants of former tropical cyclone
Lowell to the far northwest of the islands. This will temporarily
interrupt the trade wind flow and allow for sea/land breeze
circulations to develop each afternoon Thursday through Sat. Expect
possible periods of afternoon/early evening showers...especially
over interior and leeward areas.
For the long range forecast...the surface high strengthens north-northeast of the
Aloha state with the trades gradually return to moderate levels sun
into Monday. This will bring back a trade wind weather regime early
next week with showers favoring windward and mountain
areas...especially at night.
a moderate trade wind flow will produce periods of MVFR ceilings and visible
over windward slopes as showers come in. Phto and phli will briefly
experience these conditions at times tonight...and phko will see
some nearby shower activity before midnight. Otherwise...VFR will
prevail. No airmets are anticipated.
an increasing easterly long-period swell from Hurricane Marie is
expected to arrive late Wednesday and continue to build through
Thursday night. This swell will bring advisory level surf to east
facing shores. Also...an increasing south-southwest swell is
anticipated for Wednesday night into Thursday...bringing near
advisory level surf over south facing shores through Friday. Strong
currents could also develop with the arrival of these swells. The
surf should begin subsiding Saturday and continue to decline through
early next week.
With winds expected to diminish further...no Small Craft Advisory
conditions are expected through the Holiday weekend. However...the
long period easterly swell mentioned above could produce unusual
conditions in east facing channels and harbors.