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Hawaiian Islands Synoptic Discussion and Guidance

474
FXHW60 PHFO 140639
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
839 PM HST Wed Nov 13 2019

.SYNOPSIS...
A weak ridge north of the state will maintain light winds and
mostly dry weather through Thursday. A trend towards wetter
weather will begin Friday through the weekend as a weak front
stalls near Kauai and tropical moisture moves in from the
southeast.


&&

.DISCUSSION...
A weak ridge north of the state will maintain a light background
wind flow across the islands through Thursday. Land breezes will
allow clouds to dissipate over the islands and temperatures to
cool off to near normal lows for this time of year. Mostly sunny
skies will prevail Thursday morning with sea breezes setting by
midday and bringing some clouds over the island interior sections.

Starting Friday, a front will approach Kauai from the northwest.
Meanwhile, a weak surface trough will reach the Big Island from the
east. This will bring increasing chances of showers over both
Kauai and the Big Island on Friday. Drier weather is expected for
Maui County and Oahu, but a few showers will remain possible
during the afternoon. Daytime sea breezes and nighttime land
breezes will continue for all islands into Friday.

The front is then expected to stall and slowly dissipate near
Kauai Friday night and Saturday. The moisture band associated
with the surface trough to the east will stall out near the Big
Island or Maui County on Saturday night while gentle to moderate
trade winds build back in. The upper level dynamics will begin to
increase Saturday night into Sunday as a trough moves over the
state. This upper trough is likely tap into the the low level moisture
in place over the islands and increase the shower intensity.

There is large uncertainty in the forecast from Sunday and beyond
as the GFS and ECMWF show a cutoff upper low forming within the
trough and digging southward towards the islands. However, the
models place this feature in different places and would focus the
dynamics either over or to the east of the islands. We have a
slight chance of thunderstorms statewide for Sunday and Sunday
night, but will likely fine tune the timing/location with better
model consistency as the event approaches. The ECMWF keeps the
upper low over the islands into the first half of next week while
the GFS swings it eastward and shows a ridge building in, thus, a
low confidence will continue.


&&

.AVIATION...
Widespread VFR conditions will prevail through Thursday night, as
a weak, stable easterly trade wind flow holds through tonight and
shifts to the southeast Thursday. Land breezes will generally
clear skies over land tonight, with afternoon sea breezes bringing
isolated MVFR CIG over interior terrain Thursday. No AIRMETs expected.


&&

.MARINE...
Light easterly flow will transition to a southerly flow on
Thursday as a front approaches from the northwest. This southerly
flow will persist through Friday night before some northeast winds
start to develop Saturday as the front stalls out over the
western end of the state. Sunday looks to bring some strengthening
easterly winds that could approach Small Craft Advisory (SCA)
levels Sunday and Monday over the typically windy waters around
Maui County and the Big Island.

We are monitoring the new north-northwest swell that is expected
to reach the islands Thursday. The swell is just starting to
arrive at buoys 51001 and 51101, so will be monitoring the arrival
overnight to fine tune the event. The surf generated by this swell
is expected to peak at advisory levels. Advisory level surf will
reach Kauai first and could reach there as early as early
Thursday afternoon based on the latest guidance, and a couple
hours later for Oahu and Maui County. This swell is currently
expected to peak Thursday night and then lower gradually Friday
and Saturday. As mentioned above, will be monitoring the buoy
reports overnight to fine tune the timing, but will likely issue
the High Surf Advisory with the morning package.

A larger northwest swell is expected to arrive on Saturday, peak
Saturday night, then lower gradually Sunday and Monday. Surf
heights may reach low end warning levels during the peak of this
swell. Seas generated by this swell are expected to reach Small
Craft Advisory levels over waters exposed to this swell.

A series of small southerly swells are expected through the
weekend. Surf will remain small along east facing shores due to
the light winds over and upstream of the state. Surf heights will
likely rise by early next week as high pressure builds in to our
north.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...Foster
AVIATION...Birchard
MARINE...M Ballard

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



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