textproduct: Honolulu

SYNOPSIS

Today will be a transitory day from a more wet to an overall drier pattern across the island chain. Trades will be the dominant wind as scattered showers focus along windward and upslope mauka areas. Trade weather will continue this weekend with a front passing across the state from the north early next week. Relatively cooler and drier weather is expected in the front's wake early next week.

DISCUSSION

Energy within the southwest steering flow...ahead of a near stationary mid to upper level weakening low churning approximately 1,100 miles southwest of the state...has been passing across Hawaii overnight. Evidence of this was the blow up of thunderstorms over eastern Big Island's coastal Puna District and surrounding waters early this morning. We are still under a very moist air mass of between 2.1 to 2.6 inch precipitable waters that fall in the maximum climatological categories for late October standards. 12Z soundings show a more stable column over Lihue with a weak 8k ft inversion while Hilo's profile is much more unstable (~800 J/kg**2 MU CAPE and about 30 kt of ingested low level shear). This is to be expected by witness to the MCV-like convection that occurred over Puna and surrounding waters past midnight. Weak mid level ridging will be over the state today as the aforementioned low slowly slides off stage left. The synoptic movement of these primary players should limit any mid to upper level forcing over the islands as the energy east of low should remain well west of the state. The surface trough that has been over us the last few days has become diffuse enough to be unmentionable and recent ASCAT passes verifies that the state is under a light to moderate trade flow pattern. This moisture-rich resident air mass is going nowhere soon so expect more clouds than sun and scattered windward-focused showers through the day.

Halloween's forecast calls for a typical October day by Hawaiian standards albeit a touch more humid than many would like. Trades will weaken a bit and this keep conditions more muggy through the partly (leeward) to mostly cloudy (windward) day. Evening conditions should be more treat than trick with average middle 70s, 60 to 70 %RH, calm to very light trade breezes under partially cloudy skies. The highest rain chances will be over the windward exposures of all islands, especially eastern Big Island. Any passing shower will be infrequent and a quick hitter.

A central North Pacific trough will swing down and pass east of the state Sunday. This will likely push a weak surface front across the island chain late that night into early Monday. Strong backing high pressure building behind this weak boundary will produce strengthened northerly winds from late Sunday through the middle of next week. Possible sweater weather as cooler and drier air advects in from the north early next week. Post-frontal dew points lowering into the lower 60s Monday with a stout north northeast breeze will be a noticeable more autumn-like change from these recent wet and more humid conditions. A typical trade-like precipitation pattern as infrequent showers affect windward communities and upslope mauka regions. Next week will be one of generally quiet trade weather. During the end of next week, an area of disturbed weather far southeast of the islands will be monitored for the potential development of a tropical cyclone.

AVIATION

SHRA activity has significantly diminished over the past few hours, with the exception of windward Big Island. Thunderstorms near PHTO keep regenerating and have led to a stretch of IFR cigs/vis. Otherwise, conditions are largely VFR across the board. Trade winds return today with typical VCSH chances through the period.

AIRMET Sierra for mountain obscuration remains in effect abv 020 for north through east areas from Oahu to Big Island. Conditions may improve enough through the morning to allow for the cancellation of AIRMET Sierra, but planning to leave it in place for now.

AIRMET Tango for turbulence is no longer in effect. However, continuing to monitor the potential for low level light-mod turb state wide.

MARINE

A weak trough near the eastern end of the state that has been a focus for showers and thunderstorms over the past few days will slowly move southward and dissipate today. Therefore, expect shower and thunderstorm coverage to gradually reduce over the next 24 hours. Ridging to the north will gradually drive moderate to fresh easterly winds over most waters today into the weekend. A Small Craft Advisory will likely be needed late this weekend into early next week due to a combination of increasing trade winds and seas of 10 feet or greater as a result of an incoming north- northwest swell.

A small, short period north-northeast swell will fill in today and maintain small surf along north-facing shores. A larger, long- period northwest swell will begin to arrive late Saturday. This swell will likely push north and exposed west shore surf above the High Surf Advisory threshold Sunday into Monday. The swell will shift slightly more northerly and may briefly build further on Monday before dropping Tuesday. Depending on the exact direction, a Marine Weather Statement may eventually need to be issued to due the potential for harbor surges at Kahului and Hilo.

A small, medium period south swell will peak today, though surf along south-facing shores will remain below High Surf Advisory levels. This swell will then gradually decline through the weekend. During the first half of next week, south shore surf will return to below seasonal averages.

Surf along most east-facing shores will rise slightly today due to wrap from the north and southerly swells. Additionally, east- facing shorelines exposed to the larger north swell Sunday night into Monday will have the potential for advisory level surf during that time.

FIRE WEATHER

Recent rain and light winds have kept fire weather concerns low. As the soil and vegetation begins to dry out the next couple of days, fire weather conditions will move into the more moderate category. The passage of a weak front early next week will introduce breezy north northeast winds in its wake. Drier conditions are expected after this boundary's late Sunday or early Monday passage. Thus, fire weather concerns will continue to be on the rise through next week.

HFO WATCHES/WARNINGS/ADVISORIES

None.