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 becoming southwest up to 10 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 68 to 76. South winds around 10 mph. Chance of rain 40 percent.

Wednesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 86. South winds up to 10 mph. Chance of rain 30 percent.

South Side

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 87. North winds up to 10 mph shifting to the southwest around 10 mph in the afternoon. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 77. South winds around 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs around 87. Southwest winds up to 10 mph. 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. East winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 73 near the shore to around 53 near 5000 feet. Light winds. Chance of rain 40 percent.

Wednesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Central Maui

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 89. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 68 to 73. South winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 83 to 88. South winds up to 10 mph. Chance of rain 20 percent.

Upcountry

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 61 at the visitor center to around 65 at the summit. Light winds. Chance of rain 40 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 49 at the visitor center to around 45 at the summit. Light winds. Chance of rain 40 percent.

Wednesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 62 at the visitor center to around 66 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. East winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 73 near the shore to around 53 near 5000 feet. Light winds. Chance of rain 40 percent.

Wednesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. 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 with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 73 to 81. Light winds. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 67. South winds around 10 mph. Chance of rain 40 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 81. South winds up to 10 mph. Chance of rain 50 percent.

Kaunakakai

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 73 to 88. North winds up to 10 mph shifting to the south in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 75. South winds up to 10 mph. Chance of rain 40 percent.

Wednesday: Partly sunny with scattered showers. Highs 75 to 90. South winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The remnants of an old frontal boundary lay across the state today. This will maintain light and variable breezes as localized sea and land breezes play more a role the next few days. Moisture pooling up along the boundary will keep rain chances high as intermittent rain will affect most of the state. Trades will return by the weekend as the weak boundary washes out and surface high pressure northeast of the islands re-establishes a tighter downstream gradient over the region.

Discussion

This more unsettled weather pattern will hang with us the next few days as lower heights remains over the area through Friday. A pair of upper lows positioned near symmetrical north of the island chain, one approximately 900 miles northeast of the state with an weaker low about 800 miles northwest, are indirectly in control of our weather as upper ridging remains south of Hawaii. The mid level reflection of these lows, along with moisture pooling along a diffuse trough draped across the central islands this morning, will be the impetus to recurring periods of thicker, lower layer clouds and showery conditions. 12Z soundings confirm that a fairly moist boundary layer extends up to around 700 mb (~9 k ft). This is a depth that is certainly capable of providing enough moisture to support thicker clouds and higher shower probabilities the next several days. This boundary has disrupted trade flow and the benign gradient created over the state will allow more localized breezes to play a more dominant role. Thus, peaks of sunshine will enhance early afternoon sea breezes and assist in building clouds and generating more precipitation within wind-sheltered leeward areas. As the boundary becomes more diffuse and lifts a touch north through the day, the general flow will veer more southeast-south and tap into a more moisture rich equatorial air mass. This will likely increase keep rain chances on the higher side of lower-end moderate probabilities (30-40%). Higher rain chances will likely occur along the western half of the archipelago and focus along more southern coasts and upslope (leeward) mauka through Thursday. Troughing over the state will persist into late week but will fade way by Friday. Once this occurs, surface high pressure off the U.S. West Coast will exert more of an influence and re-establish a gradient better supporting light to moderate trade winds this weekend. More overcast and rain will keep afternoon maximum temperatures a degree or two lower than early October mid 80 norms while overnight drainage breezes will compensate for insulating clouds as near sunrise temperatures dip to near climate low to mid 70 standards.
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 later this week. This will provide a bit more regional stability and possibly designate 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 Tuesday as rounds of showers move in from the east on this re-established trade flow.

Aviation

A lingering diffuse old frontal boundary draped across the state has weakened regional winds and allowed pooled up moisture to initiate more frequent showers. Very light and, at times, variable winds will be dependent upon the location of the boundary wafting over the region. Due to this weak synoptic wind regime, daytime sea breezes and nocturnal land breezes will become the dominant wind pattern across many island terminals. Air fields north of the boundary will experience more easterly breezes while sites south of the boundary will have a more southerly component. The boundary is forecast to lift north through mid week and this will align statewide winds more southeasterly later in the period. A band of moisture associated with the boundary will occasionally produce tempo MVFR decks and visibilities within more moderate showers. Short-lived, isolated IFR conditions are possible within pockets of heavier rain.
In the short term, drier air will gradually fill in behind the exiting boundary and conditions will generally favor VFR. Localized breezes will still hold on through the majority of the week. Thus, daytime sea breezes will build interior clouds and produce scattered (leeward) showers while overnight land breezes will scour out decks.
There are currently no AIRMETS in effect. Tuesday's AIRMET Sierra over Oahu, Maui, Lanai and Molokai was cancelled last night due to lifting clouds and improved mountain visibilities.

Marine

A trough draped over the coastal waters will slowly drift west over the next several days and bring light to gentle south or southeast flow across all zones. This flow should also give way to localized land and sea breezes. Moderate easterly trades are forecast to fill back in by this weekend as high pressure builds far northeast of the state.
The current small, medium period, north northwest (330-340 deg) swell has been coming in slightly above guidance, as noted on this mornings Waimea Bay buoy observations. However, this swell has already peaked and should continue to slowly decline through late this week. Forerunners from the next, more significant moderate, long period, northwest swell are progged to arrive by late this weekend. During the peak of the event, early next week, 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 through late Wednesday. A small, long period, south southwest (190-200 deg) swell will fill in Thursday morning and bring a slight bump up to surf along south facing shores through late Friday. Expect below average surf along east facing shores this week as weak flow prevails.
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 may 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 4,000 to as high as 9,000 feet through mid week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov