Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXHW60 PHFO 240203
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
403 PM HST Thu Feb 23 2017

.SYNOPSIS...
Moderate to breezy trade winds will being to gradually ease over
the next 24 hours, which a further decline expected this weekend.
Limited clouds and showers through Saturday will favor windward
and mauka areas particularly of the smaller islands. Increasing
shower activity is expected starting Sunday with moisture moving
in from the south. Enhanced showers are possible as we head into
the new work week.

&&

.DISCUSSION...
No changes in the short term with the forecast this afternoon.
High pressure to the north has continued to bring moderate to
locally breezy trades to the islands. A few sites have shown a
bit of a downward trend in wind speeds over the last 24 hours.
Expecting a few more sites to show this trend over the next 24
hours. A further trend downward is expected this weekend as a
front north of the islands pushing the ridge over the islands.

Afternoon soundings from Lihue and Hilo continue to show the dry
airmass over the islands with precipitable water (PW) values of
0.68 and 0.77 respectively. Rainfall totals have remained light
with Mount Waialeale having the highest 24 hour total of 0.23
inches through 2 pm. With satellite derived PW showing the dry
airmass extending well north and northeast of the islands, expect
similar conditions into Saturday.

The models continue to agree with an increase in moisture from the
south beginning Saturday night. The front, along with its
accompanying upper level low, to the north of the state will
begin to lift north this weekend, pulling up moisture from the
south. Both the GFS and ECMWF show a surface low forming near the
Big Island early next week, but vary in placement, strength, and
movement speed. All will play a significant role into the amount
of enhanced showers we will see and for how long. The Big Island
is most likely to see the bulk of the enhancements.

PW values are expected to reach typical levels near 1.14
inches for the Big Island by Sunday morning, and continue to
climb into the middle of the week. The ECWMF brings more moisture
over the islands, with the Big Island maxing out near 1.81 inches
Tuesday night. The GFS maxes out Tuesday afternoon around 1.56
inches. The GFS develops the low and moves it quickly northward,
clearing out the islands while the ECMWF continues the above
normal PW into the second half of the week.

&&

.AVIATION...
A high pressure region north of the state will continue to bring
breezy trade winds to the Hawaiian Islands thru 24 hours. Wind
speeds will begin to decrease Friday afternoon onward as a low
pressure system drops into the region. Clouds and scattered
showers will remain focused mainly over Windward slopes and
coasts. The convective development over Big Island Interior will
taper off after sunset but may redevelop tomorrow. Isolated MVFR
conditions possible in showers, otherwise VFR conditions
prevailing all areas. 

AIRMET Tango remains in effect for low level turbulence to the
South and West of the terrain likely remaining in place through
Thursday. No additional AIRMETs are anticipated.

&&

.MARINE...
Moderate to fresh trade winds associated with high pressure to
the north of the state will continue to generate Small Craft
Advisory (SCA) conditions across channels and exposed areas around
Maui County and the Big Island. See MWWHFO (Marine Weather
Message) on our website for affected areas and specific winds and
seas expected. The SCA is in effect tonight with winds expected
to trend down thereafter.

A moderate west-northwest swell will impact surf along north and
west facing shores and will decline Friday. A larger, west-
northwest (310 deg) swell will fill in through the day Friday,
peak Friday night into Saturday, then gradually ease through the
remainder of the weekend. Advisory level surf will be likely at
and around the peak of this swell along exposed north and west
facing shores.

A small north swell will fill in Friday and hold into Saturday
before shifting out of the northeast (020-030 deg) and rising
Sunday night into Monday. As this north and previously mentioned
west-northwest swells fill on Friday night, sea heights in
exposed coastal waters north of the islands may reach the SCA
threshold and may need to issued for those affected waters.

Surf along east facing shores will maintain, or trend down
slightly this weekend as the trade winds weaken. Surf may begin
to build once again Sunday night into Monday along east facing
shores as the aforementioned small northerly swell shifts out of
the northeast.

A small long-period (18-20 seconds) south-southwest (220 deg) will
fill in during the day Friday and hold into Saturday, which may
support a slight increase in surf along south facing shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Friday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Southeast Waters.


&&

$$

National Weather Service Glossary of Abbreviations