193 
FXHW60 PHFO 060636
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
836 PM HST Tue Mar 5 2019

.SYNOPSIS... 
Locally breezy and cool trade wind conditions will continue, with
trades expected to become strong Thursday night through the 
weekend. High clouds currently in place leading to mostly cloudy 
conditions will hang around overnight, then gradually clear out 
from west to east through the day Wednesday. Outside of an 
occasional shower spilling over to leeward sections, most of the 
showers will remain focused over windward areas each day. Rainfall
accumulations will remain light with the dry air in place. 

&&

.DISCUSSION...
Water vapor imagery showed plenty of mid-level moisture streaming 
over the state from the west-southwest to east-northeast ahead of an 
upper trough positioned to the west. A band of high clouds has 
resulted, leading to mostly cloudy skies. At the surface, breezy 
trades associated with high pressure centered to the north-
northwest remain in place. A combination of the high clouds, 
breezy trades and dew points hanging around 60 degrees have led to
the cool conditions today. Radar showed the bulk of the shower 
coverage focusing over Oahu and the surrounding waters this 
evening, with some showers managing to spill over into leeward 
areas. The latest rainfall summary reflected this and showed 
mainly light accumulations over the past few hours (few 
hundredths to a tenth of an inch). Elsewhere across the state, 
quiet conditions prevail with mainly brief passing windward 
showers. Outside of a few minor adjustments to the current 
forecast to reflect the better shower coverage over Oahu this 
evening, no significant changes are anticipated in the forecast 
for the overnight period. 
  
The latest short-term guidance is lining up well the current pattern 
and supports the cool and breezy trade wind pattern continuing into 
the second half of the week. The upper clouds in place should 
gradually clear out from west to east through the day Wednesday and 
into Wednesday night as the upper trough to the west continues 
eastward. Despite the limited amount of moisture available with 
precipitable water (PW) values remaining low and dewpoints hanging 
around 60 degrees, this upper trough moving through combined with 
the breezy trades will continue to support decent shower coverage in 
Wednesday. Most of this coverage will continue to focus over 
windward areas with very little accumulations expected.  

Trades are expected to become strong late Thursday through the 
upcoming weekend as high pressure builds to the north. The 
typically windier areas around Maui County and the Big Island may 
reach wind advisory criteria by or come Friday. Showers will 
continue to focus over windward areas with some making it across 
leeward areas with the strong trades in place. 

By early next week, the surface high will weaken and move off to a 
position far northeast of the state. This will likely cause for a 
downtick in trade wind speeds. Passing light showers will continue 
to favor windward and mauka areas.

&&

.AVIATION...
VFR will be the main flying weather tonight, although there will 
be periods of MVFR ceiling and vis due to the passing showers, 
whipped up by the strong and gusty trade winds. Most of the MVFR 
conditions will be focused over the windward and mountain areas, 
but a few of these showers will slide downwind into the lee areas 
of the smaller islands before dissipating. No AIRMET Sierra, but 
will be monitoring these showers closely. Leeward Big Island will 
have an isolated shower or two this evening along the coastline. 

There is a strong inversion, sloping from 65 hundred feet over 
Kauai to 8k feet over eastern Big Island, and that is where you 
will find the tops of the low level trade wind clouds. There is a 
dense layer of high cirrus clouds, above fl200.

Strong and gusty trade winds are supported by a strong 1031 mb 
surface high, located north of the islands. We will expect more of
the same winds on Wednesday as the high shifts southeastward.
Thus, AIRMET Tango will continue until further notice.

Progs point to ocnl moderate turbulence over Hawaiian airspace 
between fl250 and fl350, exiting the area by 070000z. The
turbulence is attributed to a jet max running ahead of an 
approaching upper level trough, forecast to stall over the islands
at 070000z. So, will add this to the 10z AIRMET Tango section.

&&

.MARINE...
A Small Craft Advisory (SCA) remains in effect for all Hawaiian 
coastal waters through early Wednesday morning due to strong 
winds and elevated rough seas. Conditions may briefly drop below 
the SCA criteria across portions of the marine area from Wednesday
into Thursday, but winds will likely remain near the SCA 
threshold across the typically windy waters around Maui County and
the Big Island. The latest forecast continues to show the trade 
winds becoming even stronger from late Thursday through the 
weekend as a new surface high pressure system builds far north of 
the region. As a result, expect SCA conditions across all waters 
from Thursday night through the weekend, with gale conditions 
possible in some of the windier waters, such as the Alenuihaha 
and Pailolo Channels, particularly late Saturday through Sunday
night when the trades are expected to peak.

The current north-northeast swell will be shifting around to the 
northeast, and eventually east-northeast, as the week progresses.
A High Surf Advisory (HSA) remains in effect for elevated rough 
surf along most east facing shores. This surf may briefly drop 
below the HSA criteria. However, as the trade winds strengthen 
later this week, expect the very rough surf to reach the HSA 
criteria again along most east facing shores from late Thursday 
night through early next week.

A series of small northwest swells will continue to spread down 
across the island chain through early Friday. A large long-period 
northwest swell arriving late Friday is expected to cause surf to
approach the High Surf Warning criteria along most north and west
facing shores of the smaller islands Saturday. Guidance indicates
this northwest swell will gradually lower Sunday through early
next week, with another moderate sized northwest swell arriving as
this swell fades.

A long-period south swell arriving Friday night may produce a 
noticeable boost in surf heights along most south facing shores 
from Saturday into early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Wednesday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward 
Haleakala-Big Island North and East.

Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big 
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Wednesday for Kauai 
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi 
Channel-Maui County Windward Waters-Maui County Leeward Waters-
Big Island Windward Waters.

&&

$$

DISCUSSION...Gibbs
AVIATION...Lau
MARINE...Jelsema