Scientific Forecaster Discussion
fxhw60 phfo 230145
Area forecast discussion
National Weather Service Honolulu HI
345 PM HST Thu Jun 22 2017
weak high pressure far north of the islands will maintain light
to moderate trade winds through Friday. The trade winds will
deliver passing clouds and showers, mainly to windward areas. A
shift towards more showery weather is possible this weekend.
a dry and quiet weather pattern this afternoon across the state,
with little if any rainfall reported at the various rain gauge
locations. The weak trade wind flow with a strong capping
inversion around 8000 feet is noted on the afternoon soundings
from Lihue and Hilo. A few more clouds and showers are seen on
visible imagery upstream of the state, which will likely result in
an uptick in windward and mountain shower activity later this
Looking at the large scale weather pattern across the central
Pacific, the weak ridge responsible for our trade winds remains
stationary far to the north over the short term. Would expect a
static pattern of continued trade wind weather across our area
For the weekend, will need to watch a batch of moisture presently
further upstream of the state, as it rides in on the trades. The
surface ridge to the north will move a bit further east which will
help veer the flow more east southeasterly Saturday and Sunday,
with conditions favorable for leeward seabreezes and convection in
the afternoons. This would result in an increase in clouds and chances
for afternoon showers on the drier leeward areas. The slower
shower movement will mean a chance for higher localized rain
totals where any showers do develop. However, the airmass
stability remains in place, and should keep showers from dropping
excessive rainfall over the weekend.
By early next week, the high currently to the north-northwest will move E,
and models agree that breezy east-northeast trades will prevail, delivering
fewer showers to mainly windward areas, with the ridge aloft
strengthening over the area from the northwest.
no airmets are in effect and none are expected.
VFR will prevail, but there will be isolate MVFR ceilings over NE
sections, mainly during the night and early morning hours.
a ridge of high pressure north of the islands will keep moderate
to occasionally fresh trade winds in place through the weekend,
but winds and seas are expected to remain below Small Craft Advisory levels. The
trades are expected to strengthen early next week as high pressure
builds northeast of the islands, and scas for winds may be needed
for the typically windy waters at that time.
A new reinforcing south-southwest swell will arrive tonight, peaking near or
just below advisory levels on Friday. Surf along south facing
shores will remain above normal over the weekend and into early
next week, but below advisory levels.
In addition to the new southerly swell, tides have been running
about a half a foot above predicted levels. These elevated tide
levels will increase the risk for minor coastal flooding when
combined with the above average south swell. For the next few
afternoons, the predicted high tides are around 2.5 feet MLLW,
which does not include the extra 1/2 foot mentioned above. See the
latest Special Weather Statement (spshfo) for additional details
on the elevated tide levels and potential impacts.
Small trade wind and southeast swells will continue into the weekend, but
are expected to remain below advisory levels. In the longer
range, models indicate a northeast swell developing for the
beginning of next week. A high surf advisory may eventually be
needed for east facing shores if the swell comes in bigger than
For more details on the surf, please refer to the Oahu
collaborative surf forecast (srdhfo) prepared by pat Caldwell
under WMO header fxhw52 phfo.