Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
325 PM HST Wednesday Dec 4 2013
mainly dry and stable conditions are expected to continue across
the Hawaiian islands through the remainder of the work week and
into the weekend. Surface high pressure centered well northeast of
the area combined with a dissipating low pressure trough west of
Kauai will maintain gentle east/southeast flow across the islands.
Ridging aloft will maintain stable conditions...with rainfall
amounts remaining light. There is some potential for a wetter
pattern to develop beginning Sunday...especially across The Big
Island as moisture approaches the state from the southeast.
tranquil conditions prevail across the state this afternoon...
with area radars showing just isolated small showers mainly to
the south and west of Kauai. The 00z soundings indicate drying
and lowering inversions during the past 12 hours...with a well
established inversion down to 6000 feet at Hilo...and a weaker
inversion down to 8000 feet at Lihue. Surface analysis depicts
high pressure centered far northeast of the area...with a
dissipating low pressure trough west of Kauai...and a cold front
moving eastward near 170w.
For tonight...visible satellite imagery depicts the leading edge
of an area of enhanced cloudiness about 100 miles east of Hilo and
tracking steadily westward. This feature has a weak signal evident
on mimic-tpw imagery as well with precipitable waters up to 1.3 inches. Expect
this cloudiness to bring some showers to the windward Big Island
and possibly eastern Maui late tonight...and have boosted probability of precipitation in
those areas accordingly.
Otherwise...there is little change in the forecast reasoning for
the next few days. Middle level ridging over the area combined with
generally limited low level moisture within a weak easterly flow
regime will yield isolated to widely scattered showers...with
rainfall amounts remaining light. The flow will be weak enough to
allow for some seabreeze development across leeward/interior
sections each afternoon...but available moisture/instability will
be insufficient to allow for any significant deep convection.
As we head into the weekend...guidance continues to suggest that
a weak shear line approaching from the northwest may get close
enough to boost winds and perhaps increase rain chances a bit
around Kauai Friday night into Saturday. It seems unlikely that
this feature will progress beyond Kauai as support aloft will be
lacking...and in any case expect little sensible weather impact.
The remnants of this shear line should push back to the northwest
during the weekend...as a deep layered ridge builds to our east
along 140w...and a complex middle latitude trough develops well to
our northwest. The latest European model (ecmwf) and GFS both show a middle/upper
level trough developing southeast of The Big Island early next
week...with this feature then forecast to move northward around
the ridge to our east. There remains quite a bit of uncertainty
with this portion of the forecast...with some model solutions
brushing The Big Island with the area of deeper moisture and lift
while others keep these features confined just to the east of The
Big Island...at least into early next week. By the end of the
forecast period...the latest GFS and European model (ecmwf) push a remnant middle
level trough and area of higher moisture westward through the
state...to the south of a developing ridge to our north. Given
the relatively poor run to run consistency...have opted to make
no changes to the extended portion of the forecast at this time.
VFR conditions prevail at all taf sites with the exception of phny
where occasional MVFR conditions are occurring due to low clouds.
Expect these clouds to dissipate by this evening. There is also
some local MVFR conditions over mountainous terrain and interior
areas. Most interior areas are expected to clear out overnight. An
area of clouds just east of The Big Island may bring an increase in
low clouds and -shra over windward areas of Maui and The Big Island
afternoon reports from buoy 51101 show a gradual increase in
northwest swell. Still expect this moderate northwest swell to
peak below advisory level Thursday then gradually lower on Friday.
The wavewatch iii model continues to show multiple moderate-sized
west northwest through north northwest swells starting to impact
our area Saturday. The latest model run shows the north northwest
swell peaking Sunday through Monday below the advisory threshold.
A surface ridge will remain northeast of the area through early
next week producing mainly gentle to moderate east to east
southeast winds. Some locally fresh breezes will be possible at
times in the normally windier spots around The Big Island. Wind
speeds will likely remain below the advisory threshold.