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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 161357
Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Wed Aug 16 2017
High pressure far north-northeast of the islands will maintain
moderate trade winds over the islands at least through the rest of
the work week. Clouds and showers will favor the windward and mauka
areas under the trade wind flow. The leeward side of the Big Island
will see clouds and showers during the afternoon through the late
Trade wind weather continues across the islands early this evening
as a surface high pressure persists far north-northeast of the area.
More low clouds carried by the trades have reached the islands
overnight, bringing showers to mainly windward and mountain areas.
Satellite imagery revealed more ragged patches of low clouds are
present just east of the islands early this morning and these low
clouds will provide more passing showers to the area through rest of
the morning. Early morning Lihue and Hilo soundings stayed about the
same compared to yesterday afternoon's, with both soundings
depicting a somewhat stable air mass with low level moisture
extending to about 7k feet. Once again, expect low clouds and
showers in the island vicinity to decrease a bit later today with
daytime heating under a somewhat stable air mass.
Trade wind weather will prevail over the area through rest of the
work week, with some changes in the weather expected. The high far
north-northeast will drift further east and weaken slightly in the
next few days, then expected to remain nearly stationary over the
weekend into early next week. Therefore, expect a slow weakening
trend in the winds over the islands through the next few days, with
wind speeds easing low to moderate levels. Not much changes in the
low level moisture are expected in the next few days, though latest
model guidance still indicates an increase of tropical moisture over
the state this weekend and into early next week.
The Central Pacific Hurricane Center (CPHC) continues to monitor the
potential development of a tropical depression southeast of the Big
Island of Hawaii. As of 200 AM HST, the probability of development
within 48 hours remains medium, while the probability is high that a
weak tropical cyclone may develop during the next 5 days. For
additional information on this system, please see the latest
Tropical Weather Outlook issued by CPHC at weather.gov/cphc. Since
it is still too early to know if an organized tropical system will
actually develop, the potential changes in weather conditions over
the main Hawaiian Islands later this weekend or early next week also
remain uncertain at this time. Based on the long range forecast
models, the biggest potential impacts may be a strengthening of
trade wind speeds, plus the possibility of more organized and
persistent showers, especially over the Big Island.
High pressure northeast of the state will keep a moderate to locally
breezy trade wind flow in place through tonight. Clouds and showers
will favor windward and mauka areas, but a few showers will spread
leeward, particularly during the overnight and early morning hours.
MVFR cigs/vsbys will be possible in windward areas as the showers
move through, with PHLI and PHTO the most likely TAF sites to see
these conditions. Additionally, PHNY will likely see MVFR cigs once
the sea breeze develops later today.
AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of the mountains of all islands. The AIRMET is
expected to continue through the day today.
AIRMET Sierra is in effect for mountain obscuration across windward
sections of Kauai, Oahu, Molokai, Maui and the Big Island.
Conditions are expected to improve later this morning.
A Small Craft Advisory (SCA) remains in effect for locally strong
trade winds across the typically windy waters adjacent to the
islands of Maui County and the Big Island. The SCA is currently in
effect through Thursday afternoon. The latest forecast maintains SCA
conditions in these same areas into this weekend.
A small, long-period south swell will maintain small background surf
along south facing shores through tonight. A small, long-period
south-southeast swell is expected to fill in Thursday, peak Friday,
and then gradually subside this weekend. Another small, reinforcing
long-period southwest swell is forecast to reach the islands this
Rough moderate surf will persist along east facing shores due to
breezy trades in the vicinity of, and upstream of the islands. Surf
may trend down along east facing shores this weekend as the trades
weaken slightly. Surf will likely remain below the High Surf
Advisory criteria along all shorelines through early next week.
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office