West Side

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 85. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Lows 68 to 76. Light winds. Chance of rain 30 percent.

Thursday: Mostly sunny with isolated showers. Highs 81 to 86. Light winds. Chance of rain 20 percent.

South Side

Today: Mostly sunny with isolated showers. Highs around 87. Southwest winds around 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 77. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs around 87. Light winds. Chance of rain 20 percent.

North Shore

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 81 to 86 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 73 near the shore to around 53 near 5000 feet. Light winds. Chance of rain 50 percent.

Thursday: Mostly sunny with scattered showers. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Central Maui

Today: Mostly sunny with isolated showers. Highs 82 to 88. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 74. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 82 to 88. Light winds. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny with scattered showers. Highs around 61 at the visitor center to around 66 at the summit. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 50 at the visitor center to around 45 at the summit. Light winds. Chance of rain 40 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 62 at the visitor center to around 67 at the summit. Light winds. Chance of rain 40 percent.

East Maui

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 81 to 86 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 73 near the shore to around 53 near 5000 feet. Light winds. Chance of rain 50 percent.

Thursday: Mostly sunny with scattered showers. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Lanai City

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 81. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 67. Light winds. Chance of rain 40 percent.

Thursday: Mostly sunny with scattered showers. Highs 74 to 81. Light winds. Chance of rain 40 percent.

Kaunakakai

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 89. South winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 60 to 75. Light winds. Chance of rain 40 percent.

Thursday: Mostly sunny with scattered showers. Highs 75 to 90. South winds up to 10 mph in the morning becoming light. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A decaying trough of low pressure laying across the state will maintain light east-southeast or variable breezes through Thursday. Moisture pooled along the trough will keep moderate to high rain chances alive in the short term with the highest probabilities of precipitation focused along the western half of the island chain. Trades will return Friday as this weak trough washes out and surface high pressure northeast of the state re- establishes a tight downstream gradient over the region.

Discussion

A wet Wednesday morning for the majority of the state under weak southern steering flow. Many sites over the island of Oahu and Maui County picked up around a quarter of an inch to nearly two inches the past 12 hours from streamer showers moving up from the south. The highest rainfall has fallen over western central Oahu where the Waianae Mountains picked up over an inch since yesterday afternoon. Central Oahu has received the most overnight rain with Mililani measuring over an inch and a half of rain. Pukalani and Lahaina on the isle of Maui as well as central Molokai and Lanai, have also received their fair share of rain at around an inch since Tuesday's sunset. A welcome wetting has occurred over many areas that have been suffering through moderate to severe drought.
While showers will become less frequent the next couple of days, this unsettled weather pattern will hold through Friday. The main cause to this wet pattern has been the presence of higher moisture residing in a lower height field. Central Pacific lower mid to upper level heights within an above normal precipitable water air mass of around 1.4 inches (1.3 inch median for early October), in tandem with a diffuse low level boundary shutting off trade flow, have allowed localized breezes to interact with terrain and weak background southerly flow to provide sufficient lift in producing frequent showers. Much of the rain is traveling in from the ocean within well organized bands/cells of warm low clouds and maintaining their structure as they pass north across Hawaii. This morning's balloon soundings again confirm the existence of a deep near 8k ft moistened boundary layer. This is a depth that is certainly capable of creating thicker clouds and higher shower probabilities, even up in higher Maui and Big Island elevations, the next couple of days. The decaying broad low level boundary laying northeast- to-southwest has disrupted trade flow and the benign gradient over the state has allowed localized breezes to play more of a role. Periods of sun warming the surface under partly cloudy conditions will enhance late morning into early afternoon sea breezes. Lift generated by these breezes will build clouds that will ultimately lead to more precipitation within better wind-sheltered leeward/ southern-facing areas. As the boundary lifts north through Thursday, the general southeast-south flow will tap into a more moisture rich southern air mass and produce solid moderate precipitation probabilities. Higher rain chances within lower clouds will likely occur along the western half of the state and focus along more southern coasts and upslope (leeward) mauka. The weakness in the pressure field over the state will fade away by Friday. Once this occurs, surface high pressure off the U.S. Pacific Northwest Coast will exert more of an influence and re-establish a gradient that will produce light to moderate trades this weekend. More overcast and rain will regulate maximum low to mid 80 temperatures while overnight drainage breezes will compensate for insulating clouds as near sunrise temperatures dip into the low to mid 70s.
Mid to upper level ridging, as well as an associated drier air mass, will begin to expand up from the southeast and envelope the state. This will provide a bit more regional stability and possibly peg Friday and Saturday as the driest days of the week. Lobes of more humid air may rotate in around the southern periphery of mid-level ridging positioned northeast of the state early next week. The second week of October may not be as unsettled as this week but it appears that a more wet trade pattern sets up Sunday through mid next week as rounds of showers move in from the east on this re-established trade flow.

Aviation

A weak trough orientated southwest-to-northeast across the state has weakened regional (surface) winds and allowed pooled moisture to initiate widely scattered showers within weak southerly low to mid layer steering flow. Due to the lack of trades, microscale breezes will remain the dominant near surface wind pattern across many terminals. Higher resolution models are focusing the highest morning rain in and around Oahu and Kauai. The boundary is forecast to lift north through the day and this will align statewide winds to a south or southeast direction. Tempo MVFR decks and visibilities within more moderate showers while short lived, isolated IFR conditions are possible within pockets of heavier rain.
AIRMET Sierra for mountain obscuration is in place over Maui, Molokai, Lanai, Oahu, and Kauai early this morning due to occasional low cloud decks decreasing visibilities within showers. Conditions should improve around sunrise.

Marine

A trough draped over the coastal waters will continue to slowly drift northwest during the next several days and bring light south or southeast flow across all zones. This flow should also give way to land and sea breezes that will be observed over the nearshore waters. Gentle to moderate easterly trades will return by this weekend and continue into early next week as high pressure builds far northeast of the state.
The current small, medium period, north northwest swell will be down from previous days and continue to fade through the weeks end. Thus, surf along north-facing shores will remain near or below the October average through most of the week. Forerunners from the next, more significant moderate, long period northwest swell are progged to arrive by mid day Sunday, with the event lasting through early to mid next week. During its peak, surf along north-facing shores may approach High Surf Advisory criteria.
Background south southwest swell energy will bring tiny to small surf along south-facing shores today. A small, long period south southwest (190-200 degree) swell will fill in Thursday morning and bring a slight increase to surf along south-facing shores through late Friday.
Below average surf along east-facing shores is expected for the remainder of this week as weak flow prevails. There will be a little boost by this weekend as trades return. In addition, a small, medium to long period, easterly swell from Tropical Cyclone Priscilla in the East Pacific is forecast to arrive late Saturday into Sunday.
Peak high tides associated with the lunar cycle will lead to minor coastal flooding along shorelines and low lying coastal areas through this weekend. Coastal flooding will coincide with the daily peak tide each morning. A Coastal Flood Statement remains in effect for all coastal areas through Friday, but will likely need to be extended.

Fire weather

Weak localized and/or variable breezes and a higher frequency of showers will help maintain below critical fire weather thresholds the next several days. Inversion heights across the state will range from as low as 5,000 to as high as 9,000 feet.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov