687 
fxhw60 phfo 191416 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
400 am HST Wednesday Nov 19 2008 


Synopsis... 
expect wet trade wind weather across the main Hawaiian islands 
through tonight...with most showers favoring windward and Mauka 
areas of the islands. However...the moderate trades will 
occasionally carry some showers over to leeward sections of the 
smaller islands. Our winds will weaken and shift to a southeasterly 
direction late Thursday and Friday. Wet weather will also spread 
across most of the state Friday and Saturday...with locally heavy 
rainfall possible. 


&& 


Discussion... 
a 1027 mb surface high located near 32n 160w...or about 730 miles 
north of Honolulu...is moving east at about 20 miles per hour. The shear line 
that moved down the island has dissipated near The Big Island 
overnight. The pressure gradient south of the high pressure to the 
north of the islands and the lower pressure to the south of the 
state was producing moderate to locally fresh trade winds across 
most of the state. The trades were transporting low level moisture 
in the form of low clouds and showers to many of the islands 
overnight. These clouds and showers continued to favor windward and 
Mauka areas...but the moderate winds were carrying isolated light 
showers over to the leeward sections of some of the smaller islands. 


The strong and gusty northeasterly winds...which occurred late 
Tuesday...were likely enhanced in some locations by the rather low 
height of the inversion. This inversion was about 6500 feet in the 
Lihue sounding Tuesday afternoon. In addition...these winds were 
likely enhanced due to localized leeward downsloping. As the trades 
shifted to a more easterly direction overnight and the gradient 
south of the high relaxed...wind speeds have begun to decrease. 
Therefore...the Wind Advisory that was issued for the island of 
Lanai and for kohala on the leeward Big Island has been cancelled. 
Note...that winds will continue to be 20 to 25 miles per hour with locally 
higher gusts in these same locations for the next several hours... 
before gradually diminishing later today. 


As the surface high currently located north of the state continues 
to shift further eastward...our winds will gradually diminish from 
tonight through Thursday. Based on the most recent model runs... 
winds across most of the state will become weak from the southeast 
and south ahead of a front approaching from the northwest Thursday 
night and Friday. At the same time...a new middle and upper 
tropospheric trough is forecast to dig south toward the western end 
of the island chain. Based on this guidance...the front will become 
a surface trough just west of Kauai. The unstable atmosphere caused 
by the upper level trough...along with low-level convergence of 
moisture in the southeasterly flow over the state...may bring 
locally heavy rain to south and southeast facing slopes of Many 
Islands. These heavy rains are expected mainly on Friday and 
Saturday...but they may linger into Sunday. 


With the ground likely still damp in many locations from the recent 
precipitation...the potential for additional rainfall this weekend 
may cause some local problems. Therefore...flood potential outlooks 
are being issued by this office. 


&& 


Marine... 
moderate to locally fresh trade winds and rough seas continue in all 
of the channels...as well as Maalaea Bay and the waters south of The 
Big Island. Therefore...the Small Craft Advisory /sca/ will remain 
in effect through this afternoon. Winds and seas are expected to 
gradually diminish below the Small Craft Advisory criteria by this evening. 


The short period northeast swell combined with the moderate to 
locally fresh trade winds are expected to maintain the rough and 
choppy waves...with surf heights near the high surf advisory 
threshold along the east facing shores of Kauai and Oahu through 
today. A moderate north northwest swell is expected to build late 
Wednesday night and peak Thursday. Another moderate north northwest 
swell is expected during the weekend. Based on the latest guidance 
from the wave watch iii model...the surf heights are expected to 
remain below the high surf advisory threshold along north facing 
shores of all islands through this weekend. 


&& 


Hfo watches/warnings/advisories... 
high surf advisory until 600 PM HST this afternoon for east facing 
shores of Kauai and Oahu. 


Small Craft Advisory until 600 PM HST this afternoon for Maalaea 
Bay...the waters south of The Big Island...and all channels. 


&& 


$$ 


Houston