High Surf in Hawaii, July 5 to 8, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
352 PM HST Thu Jul 5 2018

.SYNOPSIS...
Strong high pressure far north of the area will continue to
produce rather breezy trade winds across the area through the
weekend. The high will weaken a bit early next week with trade
winds lowering just a bit. Areas of enhanced moisture riding in on
the trades will cause upticks in shower activity as the pass
across the state. Shower activity is expected to become less
frequent early next week as a drier airmass moves over the area.

&&

.DISCUSSION...
A strong 1038 mb high is located about 1400 miles north of Kauai.
This is providing the state with moderate to locally breezy trade
winds. Scattered clouds embedded in the trades is providing for a
few passing windward and mauka showers with most leeward
locations remaining dry.

A cloud band with elevated precipitable water levels up to 1.7
inches will drift over the state tonight through early Friday with
increasing windward and mauka shower activity expected. Another
area of enhanced moisture is seen several hundred miles upstream
of the islands. This enhanced moisture is forecast to reach the
Big Island late Friday and then pass across the rest of the state
Friday night through Saturday. Increasing showers primarily over
windward and mauka areas can be expected with the trade winds
sufficiently strong enough to blow some showers over to leeward
areas at times. Also, the increase in moisture along with a
slightly less stable airmass Friday night and Saturday, may allow
for a slight chance of thunderstorms over the lower east rift
zone due enhanced low level heating.

The high to the north is forecast to drift southward over the
next few days. This will result in a slight uptick in trade wind
speeds late Friday through Sunday as the pressure gradient
tightens up across the area. Wind speeds during this period may
approach Wind Advisory levels for favored locations such as the
Leeward Kohala area on the Big Island.

By Sunday, the high will be weakening with trade winds speeds
lowering back to moderate levels for the first half of next week.
Also the airmass will be a bit drier with a typical windward and
mauka distribution of showers across the area.

&&

.AVIATION...
High pressure north of the state will maintain breezy trade winds
across the islands. With the trade wind flow, expect clouds and
showers to be focused over the windward sides of the mountains.
VFR conditions are expected to prevail.

A band of showery low clouds is approaching the east side of the
Big Island and Maui this afternoon, with the northern edge about
80 upstream of Kauai and Oahu. This will likely bring an uptick
in clouds and showers tonight, which will bring some areas of
MVFR conditions.

AIRMET TANGO remains in effect for low-level mechanical
turbulence leeward of the higher terrain on all islands, and
these conditions will likely persist through tonight.

&&

.MARINE...
Over the next 48 hours, the strong surface high far north of the
Hawaiian Islands will drift south and closer to the islands. The
tightening of the pressure gradient will increase trade winds to
widespread fresh to strong on Friday and hold through Saturday
night. Due to the expected increase in winds speeds, the Small
Craft Advisory (SCA) has been expanded to all coastal waters of
the Hawaiian Islands starting Friday morning and continuing
through Saturday night. The surface high weakens on Sunday,
resulting in a decrease of the trade winds, which will lead to the
scaling back of the SCA.

The combination of strengthening trade winds and the expected arrival
of a long period swell from a distant East Pacific Hurricane Fabio
will push the east shore surf to High Surf Advisory (HSA) levels on
Friday and hold through Saturday. The trade winds and the long period
east swell is expected to ease off on Sunday. The current south swell
will continue to fill in overnight and is slated to peak on Friday
with a 3 foot swell and 14 second period, which is just below the HSA
level for south facing shores. A slow decline will follow over the
rest of the weekend. There is no other significant swell from the
south through the middle of next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory from 6 AM Friday to 6 AM HST Sunday for Kauai
Windward-Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-
Windward Haleakala-South Big Island-Big Island North and East.

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

Small Craft Advisory from 6 AM Friday to 6 AM HST Sunday 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...Burke
AVIATION...M Ballard
MARINE...Kino/Foster