Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Honolulu HI
830 PM HST Friday Apr 18 2014
a trade wind weather pattern will continue through the next
several days across Hawaii...thanks to high pressure north of the
state. Clouds and passing showers will favor windward and Mauka
areas with a few showers possible over some leeward locations.
radar and rain gauge data indicate that shower activity has
remained focused primarily across the typically wetter windward
and Mauka areas during the past several hours...but light rainfall
amounts have occurred at some leeward spots. The 00z soundings
show a rather high inversion based near 9000 feet. The deeper
moist layer beneath the inversion allows for precipitable waters to be near or
above normal...with the Lihue precipitable water just above the 75th percentile
for this time of year. Satellite imagery depicts abundant high
level cloudiness streaming northward across the state...to the
east of a middle/upper level trough centered several hundred miles
to the southwest. At the surface...a 1024 mb high is centered well
northeast of the state...with a slightly stronger high well to our
For the overnight period into Saturday morning...mimic-tpw
satellite imagery and model data suggest that a slightly drier
Lower/Middle level (850-700 mb) airmass will spread across the state
from the east. Model soundings show a lowering of the inversion
during this time as well. Therefore in the near term would expect
trade showers to remain somewhat active through the rest of this
evening and into the overnight...then become more limited in extent
with lighter rainfall amounts toward sunrise and into Saturday.
Through the rest of the weekend and into early next week...high
pressure will strengthen to the north of the state...causing an
uptick in the trade wind flow from Sunday through Monday. 850-700
mb layer moisture is forecast to increase once again during that
time as well. Aloft...guidance indicates that the middle/upper
trough to our southwest will shear apart...with the middle level
trough moving to the west southwest and away from our area...while
the weakening upper level trough drifts slowly to the east
northeast. A deep dry layer will persist across the state in the
middle levels...with a middle level ridge building just to our north
Monday through Tuesday. Therefore would expect the only impact to
our sensible weather from the upper trough to be continued high
level cloudiness...with showers favoring windward/Mauka areas.
Trade showers may be enhanced somewhat from Sunday through early
Monday due to the increasing trades and deepening moisture.
Little change is expected during the middle of next week...with
ridging at the surface and aloft remaining north of the state and
trades continuing. Continued weakening of the nearby upper trough
and the proximity of the middle level ridge may lower the inversion
somewhat and produce a slightly drier pattern...with limited
showers continuing windward and Mauka.
a trade wind flow continues with embedded showers favoring the windward
and mountain areas. Thus we will be monitoring closely for widespread mountain
obscure due to these shower bearing clouds that may warrant an airmet
Sierra. Cloud bases are down to as low as 1500 feet.
A few of these showers will drift over onto the leeward sections of
the smaller islands but they should not warrant any airmets.
Airmet Tango for low level mechanical turbulence will continue through
at least 16z Saturday.
Otherwise...VFR is the prevailing flying conditions.
a Small Craft Advisory remains posted through Sunday afternoon for
the typically windy waters around Maui and The Big Island. This
advisory will likely need to be extended into early next week as
moderate to fresh trade winds are expected to continue into the
foreseeable future. It is possible that some of the other channels
may need to be included in the advisory as well from Sunday
through Monday when trades are forecast to increase slightly.
The current small northwest swell will continue to lower overnight.
Another small northwest swell is expected to fill in during the
weekend...but the resulting surf will remain well below advisory
levels. Trade winds will continue to produce short period choppy
surf along east facing shores...and there is some potential for
minimal advisory level surf on those shores by Monday.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island leeward waters-Big
Island southeast waters.