Heavy Rain in Hawaii, August 9, 2018

Area Forecast Discussion...UPDATED
National Weather Service Honolulu HI
433 PM HST Thu Aug 9 2018

.UPDATE...
Isolated thunderstorms were added to the forecast for the Big
Island through this evening based on the radar trends and
lightning detection.

&&

.SYNOPSIS...
Deep moisture lagging behind Hector is currently moving onto the
islands, resulting in showery trade wind weather through tonight.
A drier airmass will overspread the state from east to west on
Friday, with a drier and more typical trade wind weather pattern
continuing through the middle of next week.

&&

.DISCUSSION...
Hurricane Hector remains a major category 3 hurricane around 415
miles southwest of Honolulu and continues to track away to the
west at 16 mph. Meanwhile, a 1025 mb high is located around 1300
miles north of Kauai. The resulting pressure gradient between
these two features is producing breezy trade winds across Hawaii
this afternoon.

A band of deep tropical moisture is currently anchored over the
island chain. This is creating cloudy skies with persistent, and
sometimes heavy showers, particularly across all of the windward
slopes. The trade winds are keeping the showers moving along and
not anchored over the same areas. 00Z soundings show precipitable
water (PW) values of 2.22 inches at Hilo to 1.67 inches at Lihue.
Some instability is present in the Hilo sounding with 781 J/kg
mixed layer cape, but a midlevel inversion is observed in the
Lihue sounding. Not surprisingly, radar shows the most
significant rainfall over the Big Island and Maui. Typical
rainfall amounts were around 0.25 to 1.5 inches since noon today.

On Friday, a drier airmass will push east to west across the state
and we will slowly turn to a more typical trade wind weather
pattern by this weekend. High pressure north of the state will
slide eastward on Friday, then set up northeast of the islands
over the weekend through early next week. Winds will taper off
tonight with moderate trades persisting through the middle of next
week.

&&

.AVIATION...
An area of extensive low level moisture will continue to move
across the state tonight. AIRMET Sierra remains posted
for all windward slopes and will likely remain in effect through
tonight. The moisture extends along the far northeast flank of
Hurricane Hector, which is located over 350 nm SW of Oahu and
moving away from the state. The moisture will produce widespread
MVFR ceilings and visibility, and even brief IFR conditions, over
windward slopes through tonight. A few showers spill over to
leeward areas. Subsidence aloft is producing a weak cap on the
moisture, but there have been a few heavy showers and
thunderstorms today, mainly across windward and interior Big
Island. Isolated heavy showers will be possible along windward
areas tonight.

A breezy trade wind flow will remain in place. AIRMET Tango for
TEMPO moderate low level turbulence remains in effect to the lee
of all terrain.

&&

.MARINE...
Hurricane Hector, located about 350 nautical miles southwest of
Lihue, is moving west around 14 knots. The strong pressure
gradient, between the high pressure to the north and Hector
passing south of the western end of the state will continue to
support rough boating conditions across the Hawaiian waters. Thus,
a Small Craft Advisory is in effect for all coastal waters
through tonight. A return of a more typical trade wind pattern is
anticipated Friday through the upcoming weekend as Hector tracks
away from the state and the gradient weakens.

Swell from Hurricane Hector is now on its decline, but is still
bringing elevated surf to south facing shores this afternoon. The
High Surf Advisory is in effect for south facing shores of Kauai,
Oahu, Molokai, Maui and Lanai through tonight and will likely be
cancelled by tomorrow morning as Hector continues to move westward
and away from the islands.

See the latest Oahu Surf Discussion (SRDHFO) for additional details
on surf and swell from distant sources across the Pacific expected
to impact the local area.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for south facing shores
of Kauai, Oahu, Molokai, Lanai, Maui and Kahoolawe.

Small Craft Advisory until 6 AM HST Friday for all Hawaiian
waters-

&&

UPDATE/DISCUSSION...Foster
AVIATION...Wroe
MARINE...Kino