753 
FXHW60 PHFO 211327
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
327 AM HST Fri Jun 21 2019

.SYNOPSIS...
Winds will weaken and shift around to the southeast today through
the middle of next week, leading to daytime sea breezes and 
overnight land breezes. Trade winds may return late next week. 
The current pattern of clouds and showers favoring windward and 
mauka areas will transition to one favoring increased clouds and 
rainfall across interior and mauka areas each afternoon and 
evening. Rain chances may increase across the western end of the 
state next week.

&&

.DISCUSSION...
Currently at the surface, a 1032 mb high is centered around 1850
miles northeast of Honolulu, while a surface trough is located 
around 525 miles northwest of Kauai. The resulting gradient across
the island chain is producing light to moderate trade winds early
this morning. Aloft, a broad north-south oriented upper trough is
located far northwest of the islands roughly along 170W. Infrared
satellite imagery shows a mixture of low and high clouds, 
resulting in partly to mostly cloudy conditions across the state. 
Radar imagery shows scattered showers moving into windward areas,
with some showers also moving up into the south shore of Oahu. 
Main short term concerns continue to revolve around the 
diminishing trade winds and rain chances over the next couple 
days.

Today through Sunday night, 
Model solutions are in good agreement showing the upper trough 
amplifying and cutting off into a closed upper low over the next 
couple days in the vicinity of 30N 170W. This will sharpen up the 
surface trough to the west of the islands with a couple surface 
lows developing along the trough, dragging the boundary and 
associated deep moisture closer to the state. The trades will 
hold on this morning, then shift around to the southeast this 
afternoon, with moderate southeasterly boundary layer flow then 
holding in place through the remainder of the weekend. The 
southeasterly winds will keep the smaller islands in the shadow 
region of the Big Island, resulting in lighter winds featuring 
daytime sea breezes and overnight land breezes. The airmass will 
remain fairly dry and stable through the period, with showers 
favoring coastal areas at night and interior and mountain areas 
during the afternoon and evening hours. Periods of scattered to 
broken high cloud cover will continue to move through the region,
keeping partly to mostly cloudy conditions in place through the 
weekend.

Monday through Thursday, 
Both the GFS and ECWMF remain in good agreement with the large 
scale synoptic features through the period. The upper low 
northwest of the islands will open up and lift northeastward early
next week, and this is expected to drag a weakening surface 
trough eastward and closer to the western end of the state. High 
pressure then appears to strengthen northeast of the islands late 
next week. As a result, we expect a continued light to moderate 
southeasterly flow to hold on through the middle of next week, 
with daytime sea breezes and overnight land breezes expected in 
most areas of the smaller islands. Moderate trade winds could then
return Thursday.

As for forecast details, model solutions have trended closer to
the islands with the surface trough and associated deep moisture 
during the first half of next week. As a result, rain chances have
been adjusted higher over Kauai and Oahu through Wednesday, with a
transition over to more of a trade wind pattern expected Thursday.
Showers will continue to favor locations near the coast at night 
and during the morning, and interior and mountain areas during the
afternoon and evening. Considerable cloudiness is expected 
through the period. Additionally, there could be a tap into deep 
tropical moisture during the early to middle part of next week, 
which could bring the potential for some locally heavy rainfall 
and thunderstorms. Will leave mention of heavy rain and 
thunderstorms out of the forecast for now and monitor future model
trends closely.

&&

.AVIATION...
A 1032 mb surface high resides far northeast of the State, while 
a trough approaches from the northwest. This pattern will 
maintain light to locally moderate southeast flow across the main
Hawaiian Islands. The air mass over the state remains mostly dry 
and mostly stable with a notable subsidence inversion around 6000 
ft. Expect ragged clouds and scattered light showers to remain 
focused along east facing slopes coasts. 

The weak flow will allow light sea breezes to predominate across
leeward coasts in the afternoon and early evening hours. Light
land breezes during the overnight and early morning hours will 
encourage partial clearing along leeward coasts at night. Low 
topped cumulus buildups will likely redevelop over interior Big 
Island this afternoon.

No AIRMETs are currently in effect or anticipated at this time.

&&

.MARINE...
Trades will continue to trend down and shift out of the southeast
today as the ridge drifts southward into the area in response to 
low pressure developing along a trough northwest of Kauai. This 
transition will allow localized land and sea breeze conditions to 
setup near the coasts each day through early next week. Although 
the forecast confidence this far out remains low, trades may not 
return until late next week.

Surf along south facing shores will remain small through early
next week with mainly a combination of short-period southeast
trade wind energy and overlapping background southerly swells
moving through. 

For the long range, guidance continues to advertise a gale- to 
storm-force low passing south to southeast of New Zealand over 
the upcoming weekend with seas forecast to reach the 35 to 45 ft 
range. If this scenario materializes, a decent south swell will 
become a possibility locally at the end of the month through the 
first couple of days in July.

Surf will continue to trend down today as the trades ease and
shift out of the southeast. An upward trend, however, is 
anticipated over the weekend as a moderate period (10-12 seconds) 
northeast swell from a recent pocket of strong breezes that setup 
within the 040-060 degree band relative to the islands over the 
northeast Pacific moves through. Heights should remain below the 
advisory level for east facing shores through the peak this 
weekend.

&&

.FIRE WEATHER...
Fuels remain drier than normal, with the Keetch-Byram Drought 
Index (KBDI) above the Red Flag Warning threshold of 600. While 
we're not expecting to reach Red Flag thresholds today, dry 
conditions will continue, keeping fire danger elevated. Decreasing
winds and increasing humidity levels will lower fire danger over 
the weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Jelsema
AVIATION...Bedal
MARINE...Gibbs