000 
fxhw60 phfo 250626 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
826 PM HST Thu may 24 2018 


Synopsis... 
breezy trade winds are expected to persist through Friday night, 
which will focus clouds and showers over windward areas. The Lee 
areas of the smaller islands can expect a few passing showers. 
The trades are expected to ease somewhat over the weekend through 
early next week. An uptick in trade showers may happen on Friday 
night and Saturday, with additional showers on tap for Monday or 
Tuesday of next week. 


&& 


Discussion... 


A high pressure system is now 1000 miles north-northeast of Oahu this evening, 
and continues on its eastward trek. By Friday evening, the high 
will be 1200 miles NE of the islands, far away enough where the 
breezy trade starts to weaken. We anticipate the rather widespread 
moderate to strong trades to retreat to the typical windy areas 
of Maui County and The Big Island by Saturday. A new high pressure 
system will set up further north of the islands Monday, and move 
to the east during the first half of the new week. This will 
continue to keep trade winds on the lighter side. 


An uptick in trade showers is expected Friday night and Saturday 
morning as the remnants of an old front passes through the 
islands. We anticipate a somewhat of a dry Saturday afternoon. 


An upper level trough about 1000 miles west of Kauai this evening 
is expected to move to the east through the weekend, stalling 
west of Kauai during the first part of the new week. The European model (ecmwf) and 
GFS are in good agreement with this upper level feature, but 
differ on some of the effects on the islands. The proximity of 
the upper trough, though, will be close enough to the islands to 
destabilize the air mass, particularly the Western Islands, which 
at the very least means some enhancements to the showers over the 
islands during the first part of the week. We are awaiting the 
latest European model (ecmwf) solution, to see how well it compares to the GFS. 
The GFS shows the upper trough about 360 miles west of Kauai Monday 
morning, with the 500 mb temperature at around minus 11 c over 
Kauai. This is just enough to support a slight chance of a 
thunderstorm for Kauai. It also safe to say we expect showers, 
and rainfall totals to increase compared to what we have seen 
over the last couple of days. 


&& 


Aviation... 
mainly VFR conditions are expected for all taf sites through 
Friday, though passing low clouds and showers may bring brief 
MVFR ceiling and visible conditions along the windward areas. There 
may be enough low cloud coverage at times to warrant airmet mountain 
obscure along the windward slopes, but none is needed so far. 


Brisk trade winds will persist across the area through Friday but 
ease slightly as a strong high pressure far north-northeast of the 
islands continues to advance east. Airmet Tango series remains 
posted for low level turbulence over and immediately south and 
west of mountains below 8000 feet on all islands. These conditions 
are expected through Friday. 


Periodic explosive eruptions at Kilauea/Halemaumau crater continue 
to produce billows of volcanic ash at times, with the plume of 
emissions predominately rising to slightly above the inversion 
level and spreading to the southwest over Kau district on The Big 
Island. MVFR visible can be expected in this area and significant meteorological information Tango 
series for volcanic ash remains in effect. 




&& 


Marine... 
high pressure north-northeast of the state will keep breezy trade 
winds in place across the marine area through Friday night. The 
trades will trend down over the Memorial Day weekend as an 
approaching front shifts the high further eastward and away from 
the islands. The trades will begin to strengthen on Tuesday as a 
new high builds north of the state, with breezy conditions 
returning for the middle and latter part of next week. A Small 
Craft Advisory (sca) remains in effect for all marine zones east 
of the Kauai Channel with the exception of the windward Big Island 
waters through 6 am Friday. Small Craft Advisory conditions are expected to 
continue for the typically windy waters around Maui and The Big 
Island through Friday night, and this Small Craft Advisory may eventually need to 
be extended through the day on Saturday. 


Surf will remain below advisory levels along all shores through 
at least the middle of next week. A series of south-southwest 
swells will keeping surf along south facing shores near the 
summertime average. Rough surf along east facing shores will 
subside over the Memorial Day weekend as trade winds weaken 


&& 


Hfo watches/warnings/advisories... 
Small Craft Advisory until 6 am HST Saturday for Maalaea Bay, 
pailolo and alenuihaha channels, and waters south of The Big 
Island. 


Small Craft Advisory until 6 am HST Friday for the windward and 
leeward waters of Oahu and Maui County, and the Kaiwi Channel. 


&& 






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