Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
400 am HST Thursday Mar 5 2015
a cool air mass with low clouds will prevail into the weekend from
Niihau to Maui. Showers will be lighter than earlier in the week...
and will occur mainly over windward slopes. Over The Big Island...
the rain and deep clouds will diminish gradually through the
weekend. Northeast winds will persist throughout. Another rain band
may affect the state early next week.
deep cloud layers shifted southeast...exposing the main Hawaiian
islands from Niihau to Maui...but remaining thick over The Big
Island. Shallower stratocumulus clouds filled in rapidly behind the
deep layers though...keeping more cloud cover over the smaller
islands than expected earlier. Thanks to orographic forcing...these
lower clouds still managed to produce locally substantial
precipitation despite the relatively dry air mass now in place over
the smaller islands. Probability of precipitation...clouds...and related fields have been
adjusted accordingly. Over The Big Island...the air mass remained
relatively moist...and certainly saturated...through a large part of
the atmosphere. Winds across the state were a little too northerly
to be called proper trade winds...and speeds too high to be called
Aloft...the cold pool associated with an extension of the broader
low located well to the northeast contributed to the instability
driving the weather across the state...though the trough had become
less sharply defined overnight.
Although the deep cloud layers have left Maui County...some
solutions portrayed a gradual decrease in precipitation and cloud
cover there. One possibility may be that the cloud layers will shift
north again briefly...as satellite data suggested...before fraying
slowly there and over The Big Island through the rest of the week
and into the weekend...with showers following this trend as well. In
any case...Kauai County and Oahu will spend most of the rest of the
week under the cold-air cumuli...and perhaps the showery
Guidance generally predicted a pair of fronts to crash into the
surface high to the north...diminishing wind speeds slowly over the
state through the next 60 hours. Wind direction should remain a
little to the north of climatology though.
Solutions started to drift apart by early next week. However...some
models predicted a lobe of the middle-level low to sweep over the
islands again...providing uplift and reducing stability. Guidance
did agree that water vapor would accumulate along the boundary
between the air masses again by that time. The support from aloft
may enable the boundary to shift north over the state again...
potentially bringing a repeat of the past few days. However...recent
runs have tended to keep the boundary...and thus the heavy
precipitation...south of the state.
a Small Craft Advisory remained in effect for strong trade winds and
rough seas over typically windier coastal waters around the state.
Rough surf will build along east-facing shores later in the week...
possibly requiring a high surf advisory. A north swell arriving
Sunday may produce advisory-level surf along north-facing shores.
Otherwise...surf should remain below the advisory thresholds through
Small Craft Advisory until 6 am HST Saturday for Kauai northwest
waters-Kauai leeward waters-Kauai Channel-Kaiwi Channel-Maalaea
Bay-Pailolo Channel-Alenuihaha Channel-Big Island leeward waters-
Big Island southeast waters.