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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 140645

Area Forecast Discussion
National Weather Service Honolulu HI
845 PM HST Sun Jun 13 2021

Moderate to breezy trade winds will continue this week. Low
clouds and showers will focus over windward areas, with showers
more active during nights and mornings. Daytime heating will
produce clouds and a few showers over the leeward slopes of the
Big Island during the afternoons and evenings. Increasing rainfall
is possible by midweek.


Have made some small adjustments to the PoPs and associated fields
for tonight, mainly to lower rain chances, particularly over Kauai
and Oahu based on satellite and radar. Satellite shows mostly
clear skies over and immediately upstream of those islands this
evening. Some increase will be expected as the night wears on, but
most of the clouds and limited showers will be focused over the
windward sides of Maui County and the Big Island.

High pressure north of the islands will maintain a moderate to
breezy trade wind flow through much of the week. Satellite
derived precipitable water (PW) continues to show PW values around
1 inch near the islands, and rainfall totals reflect lighter
amounts from the showers riding in on the trade winds. A band of
increased PW is about 240 miles northeast of the smaller islands.
Expect this moisture to reach the islands tomorrow or tomorrow
night and could help to boost some rainfall totals.

The high is expected to move eastward across the north central
Pacific as a complex low and front linger near the dateline. Look
for clouds and showers to remain focused over windward areas, with
some making it to leeward areas from time to time. An upper low
northwest of the islands is forecast to move toward the state
over the next few days as a separate frontal boundary approaches
from the north. This would lead to an increase in shower coverage
and intensity starting Tuesday night, initially for Kauai and
Oahu, and then spreading to Maui County over the second half of
the week. Trade winds will continue through this time period, so
showers will remain focused over windward and mountain areas.


Moderate easterly trades will continue through Monday, with
clouds and showers favoring windward coasts and slopes. MVFR
conditions will be possible in and around showers moving through,
especially through the late night and early morning periods.

There are no AIRMETs currently in effect, however, AIRMET Sierra
can't be ruled out later tonight through early Monday morning for
mountain obscuration over windward areas.


High pressure north of the islands maintain moderate to fresh
trade winds over most of the coastal waters through next weekend.
Winds may reach Small Craft Advisory thresholds at times around
Maui and the Big Island.

Surf along south facing shores will remain small through
Wednesday, then build, possibly reaching High Surf Advisory
levels next weekend. A short-period north swell will produce small
surf along north facing shores tonight through Wednesday night.
Surf along north facing shores will be minimal through the rest of
the week. A small northwest swell is possible early next week. Trade
winds upstream of the islands will produce small and choppy surf
along east facing shores through the week.






Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
Send comments to: Ryan Lyman