Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 211410
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Tue Aug 21 2018

.SYNOPSIS...
High pressure north of the state will provide for a typical trade
wind weather pattern across the area today. Clouds and passing
showers will favor windward and mauka areas with just a few brief
showers expected over select leeward locations. For Wednesday
through the remainder of the week into the weekend, our weather
pattern will be highly dependent on the track and intensity of
Hurricane Lane.

&&

.DISCUSSION...
Please note that tropical cyclone operations are in effect. So as
to incorporate the latest forecast information from the Central
Pacific Hurricane Center (CPHC), public forecast updates from the
Honolulu Forecast Office will come shortly after forecast updates
are received from CPHC.

Typical trade wind weather continues over the islands today, with
passing low clouds and showers affecting mainly windward and
mountain areas. Both early morning Lihue and Hilo soundings showed a
typical trade wind profile, with low level moisture extending to
around 6 thousand feet. Trades will still increase slightly as highs
far northeast and northwest consolidate with Hurricane Lane to the
south. A mid level ridge over the area is bringing a rather stable
airmass to area. An almost west to east oriented area of low clouds
has reached the Big Island and Maui county overnight, and will bring
more clouds and showers to the windward and mountain areas.

Weather for the early part of Wednesday across the islands will
still pretty much be trade wind weather, though a further increase
in low clouds as well as trade winds are expected for the islands as
more moisture will reach the area from the east while Land edges
closer. As for Wednesday night through the rest of the week time
frame, our weather will be highly dependent on the track and
intensity of Hurricane Lane. It is still too early to determine the
extend of the weather impacts that Lane may have on the state. The
latest forecast track from the Central Pacific Hurricane Center
still has Lane passing south of the main Hawaiian Islands, but its
track has nudged closer to the state. If this track holds, the
potential impacts on our islands weather could include an increase
in wind speeds due to a tightened pressure gradient, between high
pressure north of the state and Lane traversing to our south.
Moisture associated with Lane would likely bring increased shower
activity with locally heavy rain possible over the Big Island,
mainly east and southeast and then eventually spreading up the
island chain through the remainder of the week. Also swell generated
by Lane could bring very large surf to the islands.

Everyone is encouraged to monitor the latest advisories on Hurricane
Lane from the Central Pacific Hurricane Center.

&&

.AVIATION...
Trade winds will strengthen as surface high pressure builds north of
the area and Hurricane Lane approaches from the southeast. Stronger
trade winds will cause moderate mechanical turbulence to develop
over and along leeward slopes of mountains across the state. AIRMET
Tango remains in effect for low level moderate turbulence.

Drier and more stable air will produce decreasing cloud and
showers trends with VFR conditions prevailing today.

Clouds and showers are likely to increase later in the week as
Hurricane Lane approaches the Hawaiian Islands. The weather
conditions across the Hawaii region are greatly dependent on the
track of hurricane.

&&

.MARINE...
Please note that tropical cyclone operations are in effect. So as
to incorporate the latest forecast information from the Central
Pacific Hurricane Center (CPHC), marine forecast updates from the
Honolulu Forecast Office will come shortly after forecast updates
from CPHC, namely shortly after 5 and 11 am/pm, instead of the
normal 4 and 10 am/pm.

A weak surface trough W of Kauai will move W away from the area
today as high pressure builds to the N. This will result in a
gradually increasing trade wind flow through today. A Small Craft
Advisory (SCA) remains in effect for the windier areas around Maui
and the Big Island for these stronger winds. As Hurricane Lane moves
into an area S of the islands by mid-week, the pressure gradient
will likely increase further, potentially requiring an expansion of
the SCA. More significantly, a Tropical Storm Watch remains in
effect for the coastal waters south of the Big Island. This may need
to be upgraded to a Tropical Storm Warning or Hurricane
Watch/Warning as the storm gets closer. There is significant
uncertainty regarding the position and intensity of Lane later in
the week, so it is too early to determine what impacts Lane may
eventually bring, and mariners need to continue to closely monitor
forecasts.

A High Surf Advisory for E facing shores of Maui and the Big Island
remains in effect. As Hurricane Lane moves into an area S of the
islands later this week, S swell will likely increase, with a wide
variety of wave periods and directions leading to rough and
potentially damaging surf. There is still significant uncertainty
and it is difficult to know the level of impacts, but there is
potential for large seas/swells from Lane leading to warning-level
surf along E through S facing shores of the islands. Otherwise, a
small NNW swell is expected to peak today before gradually
diminishing Wednesday and Thursday.

See the latest Oahu Surf Discussion (SRDHFO) for more details on
surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Windward
Haleakala-South Big Island-Big Island North and East.

Tropical Storm Watch for Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 PM HST this evening for Maalaea
Bay-Pailolo Channel-Alenuihaha Channel.

&&

$$

SYNOPSIS/DISCUSSION...Hui
AVIATION...BOHLIN
MARINE...POWELL


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