Photo Credit: Allen Tate

West Side

Today: Windy. Mostly sunny with scattered showers early in the morning, then partly sunny with numerous showers in the late morning and afternoon. Highs 73 to 83. Northeast winds 20 to 35 mph with higher gusts. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 65 to 72. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 76 to 84. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

South Side

Today: Mostly sunny. Windy. Isolated showers early in the morning. Highs around 82. Northeast winds 30 to 35 mph with higher gusts. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers and thunderstorms in the evening, then isolated showers after midnight. Lows 64 to 72. Northeast winds around 10 mph. Chance of rain 20 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Isolated showers and thunderstorms. Locally heavy rainfall possible. Highs around 86. East winds around 10 mph in the morning becoming light. Chance of rain 20 percent.

North Shore

Today: Showers in the morning, then numerous showers in the afternoon. Highs 74 to 80 near the shore to around 62 near 5000 feet. East winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 68 near the shore to 47 to 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Tuesday: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 82 near the shore to around 65 near 5000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Central Maui

Today: Mostly sunny. Breezy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs around 79. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers and isolated thunderstorms in the evening, then isolated showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 79 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Upcountry

Today: Very windy. Partly sunny with scattered showers. Highs around 57 at the visitor center to around 53 at the summit. Northeast winds 45 to 50 mph with gusts to 60 mph decreasing to 20 to 30 mph in the late afternoon. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with isolated showers and thunderstorms. Locally heavy rainfall possible after midnight. Lows around 46 at the visitor center to around 43 at the summit. East winds 20 to 25 mph. Chance of rain 20 percent.

Tuesday: Mostly cloudy. Breezy. Scattered showers and isolated thunderstorms in the morning, then isolated showers and thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 60 at the visitor center to around 56 at the summit. East winds 15 to 25 mph. Chance of rain 50 percent.

East Maui

Today: Showers in the morning, then numerous showers in the afternoon. Highs 74 to 80 near the shore to around 62 near 5000 feet. East winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 68 near the shore to 47 to 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Tuesday: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 82 near the shore to around 65 near 5000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Lanai City

Today: Windy. Mostly sunny with isolated showers. Highs 68 to 77. Northeast winds 20 to 30 mph with higher gusts. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 63. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers and thunderstorms in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 72 to 80. East winds around 10 mph in the morning becoming light. Chance of rain 40 percent.

Kaunakakai

Today: Windy. Partly sunny with scattered showers. Highs 64 to 84. Northeast winds 20 to 30 mph with higher gusts. Chance of rain 50 percent.

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 56 to 72. East winds 15 to 25 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers and isolated thunderstorms in the morning, then mostly sunny with isolated showers and thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 66 to 86. East winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An upper level low just east of the islands will move into Big Island and Maui this morning. Instability associated with this low will produce wet unsettled weather across the state. The highest rainfall amounts are forecast over windward and mountain areas favoring Molokai, Maui and the Big Island. The high pressure ridge far north of the island chain and the approaching low will produce breezy to windy trade winds today with the strongest winds over mountain and leeward areas of all islands. Trade wind speeds will slowly decrease through the week, becoming light and variable on Wednesday and Thursday. Another round of unsettled wet weather will develop from Friday into the weekend as another upper low combines forces with a cold front bringing widespread rainfall to all islands.

Discussion

Corrected first paragraph of discussion section.
The satellite imagery this morning continues to show a deepening upper level low drifting towards Maui and the Big Island. This low will continue to generate unstable cloud bands that will drift into all islands on the trade winds into Wednesday. The highest rainfall amounts in this wet trade wind pattern will favor windward and mountain areas, however even typically drier leeward communities will see periods of rainfall.
The short term forecast remains breezy and wet as this upper low tracks over the Big Island and stalls just south of Maui by Tuesday. A large pool of upper level cold air near the low center will drive the instability over all islands. Periods of heavy rain are expected along with isolated thunderstorm activity over the eastern islands of Maui and the Big Island. A fast moving jet stream on the west side of this low will move over the Big Island and Maui today, strong pressure gradients with this approaching low will produce strong and gusty winds over mountain and leeward areas of all islands. A High Wind Warning remains in effect for the highest summits on the Big Island, and a Wind Advisory is in effect for leeward and mountain portions of all islands through this afternoon. These strong upper level winds will decrease later this afternoon as the jet stream drifts westward ahead of the approaching low center. Cold air aloft will drop snow levels down to around 12,000 feet elevation with a wintery mix of snow and ice possible over the summits of Mauna Kea and Mauna Loa through Wednesday. Around 2 inches of storm total snowfall amounts are forecast over the highest summits on the Big Island through Wednesday.
The upper low will be located south of Maui on Tuesday, and the intensity of the low will gradually weaken into Wednesday. The low center will kick out to the northeast on Thursday, moving away from the state, ahead of yet another low pressure system approaching the islands from the north. The high pressure ridge north of the region will diminish as a cold frontal trough drifts into the region from the northwest.
Another strong upper level low from the far North Pacific will dive quickly south towards the Hawaiian Islands from Wednesday onward. As the low moves into the Hawaii region on Friday it will combine forces with the stalling cold front. Long range guidance continues to show these two systems merging from Thursday to Friday just north of the island chain. This combined storm will push an invigorated cold front into the islands from Friday through Sunday. The combination of the surface front and the cold air aloft associated with this next upper low may produce another round of heavy rainfall and thunderstorms across the region. The threat for flash flooding will be elevated for all islands during the Friday through Sunday time periods. However island by island impacts are highly dependent upon the upper low tracking exactly as the models predict over the next five to seven days. Slight deviations in the track of this upper low may produce significant changes to the local island weather impacts.
Global weather models remain fairly consistent on the track of the upper level low and cold front. Extended range guidance shows southerly kona winds developing across the state from Saturday to Sunday. This system may be our first kona low of the season.

Aviation

Early this morning, an upper level low and an associated surface trough continue tracking southwest towards the island chain. This upper low is expected to approach the eastern end of the state today, track over the Big Island and Maui, and then stall south of Maui over the next several days. Increasing moisture and instability will enhance shower activity today, especially for north through east facing sections of the islands. Prevailing MVFR conditions and periods of heavier showers are expected at times across windward Maui and the Big Island by this afternoon and tonight. Additionally, as stability decreases this afternoon and evening, isolated thunderstorms will be possible from Maui to the Big Island. For now, AIRMET Sierra remains in effect for tempo mountain obscuration above 2,000 feet for north through east sections of the Big Island, but this may need to be expanded later today as showers and clouds increase.
AIRMET Tango for moderate upper level turbulence remains in effect from Molokai to the Big Island early this morning, but models indicate that this should diminish over the next several hours. Additionally, AIRMET Tango has also been issued for moderate low-level mechanical turbulence below 7,000 feet downwind of the mountains of all islands. This will likely be needed through tonight as breezy to locally strong surface winds remain in place across the state.

Marine

Locally strong NE trade winds are in place this morning, due to the pressure gradient between a surface trough about 400-500 miles ENE of the islands and a surface high passing well N of the area. A Small Craft Advisory (SCA) is posted for zones through the day today, and may need to be extended in time for some areas, depending on the evolution of the trough. Little overall change is expected in the short term, but as the trough moves W through the island chain later today and tonight, winds will shift to the E and SE. These shifting winds may remain locally strong (mainly over windward waters), but there is a greater than usual amount of uncertainty associated with the short-term forecast.
The surface trough will bring an increase in showers today, some locally heavy, and the potential for thunderstorms, as a nearby low aloft destabilizes the atmosphere. The low aloft will linger over the state into midweek while gradually weakening, continuing to fuel the potential for thunderstorms and heavy showers.
The high will move far NE of the area into Wednesday while the surface trough becomes increasingly broad and diffuse as it moves to the SW of the islands. Resultant E-SE winds may remain locally strong over windward waters, with weaker winds over leeward waters. On Thursday, guidance indicates that winds may briefly trend weaker as a trough develops over the area in advance of an approaching front. Though too soon to be confident, this potentially powerful front could move through the islands late in the week, followed by strong NW to N winds. An associated strong surface low may develop a couple hundred miles N of the islands by next weekend, bringing the possibility of strong winds, very rough ocean conditions and unsettled weather.
A new NNW swell is now declining at buoys 51101 and 51001 NW of Kauai, but will peak in island waters this morning, with resultant surf remaining below High Surf Advisory levels. Today’s peak will be followed by diminishing surf through Tuesday, although a short-period NE swell is expected to arrive the next couple of days. Combined with increased trade winds near and upstream of the islands, an increase in choppy surf along windward shorelines is anticipated. Otherwise, relatively small NW swells will prevail until the end of the week, after which the potential exists for a very large NNW swell to arrive.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST this evening leeward and mountain portions of all Hawaiian Islands.
High Wind Warning until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters,

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Data Courtesy of NOAA.gov