Photo Credit: Laila Reiss

West Side

Today: Sunny. Isolated showers in the afternoon. Highs 75 to 81. Southwest winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 62 to 68. Light winds becoming south up to 10 mph after midnight. Chance of rain 20 percent.

Monday: Mostly sunny early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Highs 75 to 81. South winds up to 15 mph shifting to the southwest in the afternoon. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 81. Southwest winds up to 10 mph. Chance of rain 20 percent.

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

Monday: Breezy. Mostly sunny early in the morning, then isolated showers in the late morning and afternoon. Highs around 81. Southwest winds 10 to 20 mph. Chance of rain 20 percent.

North Shore

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 78 near the shore to around 57 near 5000 feet. West winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows 60 to 66 near the shore to 45 to 50 near 5000 feet. Light winds becoming south up to 10 mph after midnight.

Monday: Mostly sunny. Isolated showers in the late morning and afternoon. Highs 73 to 78 near the shore to around 58 near 5000 feet. Southwest winds up to 15 mph. Chance of rain 20 percent.

Central Maui

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 82. Southwest winds up to 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Lows 61 to 66. South winds up to 10 mph increasing to 10 to 15 mph after midnight.

Monday: Mostly sunny in the morning then becoming partly sunny. Breezy. Highs 77 to 83. Southwest winds 10 to 20 mph.

Upcountry

Today: Sunny in the morning, then partly sunny with scattered rain showers in the afternoon. Highs around 51 at the visitor center to around 46 at the summit. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows around 43 at the visitor center to around 38 at the summit. Southwest winds up to 15 mph.

Monday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 53 at the visitor center to around 48 at the summit. Southwest winds up to 25 mph. Chance of rain 20 percent.

East Maui

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 78 near the shore to around 57 near 5000 feet. West winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows 60 to 66 near the shore to 45 to 50 near 5000 feet. Light winds becoming south up to 10 mph after midnight.

Monday: Mostly sunny. Isolated showers in the late morning and afternoon. Highs 73 to 78 near the shore to around 58 near 5000 feet. Southwest winds up to 15 mph. Chance of rain 20 percent.

Lanai City

Today: Mostly sunny with isolated showers. Highs 69 to 76. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 64. Light winds. Chance of rain 20 percent.

Monday: Partly sunny. Scattered showers in the late morning and afternoon. Highs 70 to 77. Southwest winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Kaunakakai

Today: Sunny. Isolated showers in the afternoon. Highs 68 to 78. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 54 to 66. Light winds becoming south up to 10 mph after midnight. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs 69 to 80. South winds up to 15 mph shifting to the southwest in the afternoon. Chance of rain 30 percent.

Detailed Forecast

Synopsis

Sea breezes will bring interior showers this afternoon followed by clearing as land breezes emerge tonight. Monday through Wednesday will feature periods of showers focused over leeward zones followed by gusty westerly winds which will bring cooler and much drier conditions to the islands.

Discussion

Surface pressure falls across the islands have finally wiped out the pressure gradient enough to allow land breezes to form. While most areas have cleared out, enough low-level moisture exists to generate spotty showers along these boundaries as they push offshore. This has resulted in periodic slow-moving showers mainly over Lanai and coastal portions of eastern and southern Oahu. This is also a positive development in support of this afternoon's forecast for interior showers as inland sea breeze convergence should be much more effective than this morning's land breezes. Strengthening southwest flow aloft will tend to focus this activity over east- central to eastern portions of each island. As was the case last evening, heavy showers lingering offshore of Maui and Molokai are showing a tendency to either be stationary or shift further offshore, a sure sign of the arrival of WSW winds in the mid-levels. Going forward, pressure falls will further diminish the pressure gradient as WSW flow aloft gradually works its way down to the surface, which won't happen in any appreciable capacity until late tonight or even Monday. Land breezes will therefore bring clearing again tonight, though isolated showers will probably develop along the boundaries again tomorrow morning.
Expectations for Monday through Wednesday have changed very little. A cold front presently around 600 miles WNW of Kauai will trudge eastward the next 36 hours, reaching Kauai early Monday morning. IR shows cold cloud tops concentrating further north coincident with the the best dynamic forcing. The southern portion of the front which will affect the islands will be increasingly squashed from the top-down by upper-level subsidence which will limit the potential for very deep convection, including thunderstorms. Even so, appreciable moisture depth and pockets of conditional instability in the lowest 20kft or so will be sufficient to generate a high coverage of showers focused over leeward zones. Likewise, modest instability appears sufficiently deep that leeward terrain may be particularly effective at triggering deeper convection and locally heavy rainfall. It is worth noting that while moderate southwesterlies will focus rain over leeward areas, showers will be deep enough to regularly track over windward zones as well. This cold front will initially be a progressive feature, bringing 12 to perhaps 18 hours of increased showers to Kauai (Monday) and Oahu (Monday afternoon into Tuesday night). The moisture band will then stall over Maui County where increasing southwest winds will generate persistent or at least very frequent showers, some again locally heavy, over leeward zones of Maui and the Big Island. Overall, flash flood potential appears extremely low to nonexistent for Kauai and Oahu at this time. However, there is at least some potential over Leeward Maui and possibly Leeward Big Island a steady feed of showers with periods of higher rates along elevated terrain develops Tuesday night and continues through Wednesday.
A second, much stronger, and similarly progressive cold front will arrive quickly on the heels of the first, reaching Kauai Tuesday evening. Despite increased low-level convergence, breezy southwesterlies, and better dynamic support, loss of instability due to ongoing warm advection will be a significant moderating influence on shower intensity. Regardless, stronger mid-level forcing will quickly drive the front through the area, kicking the stalled frontal boundary out of Maui County and the Big Island as it does so.
Strong, well-mixed WSW to W winds will fill in behind the front on Wednesday. Dry advection (with a modest cold advective component) will facilitate gusty winds over Kauai and, to a lesser extent, Oahu. At this time, a wind advisory appears likely for these islands on Wednesday. Local effects due to terrain may also ultimately warrant an advisory for favored zones on Maui and the Big Island.
Slightly cooler and much drier air will fill in for the remainder the week. However, some noticeably cool overnight/early morning temps are in the cards late next week with dewpoints comfortably in the 50s as diminishing winds give way to overnight land breezes.

Aviation

Light land breezes this morning will give way to sea breezes this afternoon, with land breezes then returning tonight. Southwest winds will begin to pick up late tonight over the western end of the state in advance of a front. Showers will favor windward slopes and coasts through daybreak, with most shower activity ending over land around first light. After a mainly dry morning, daytime heating and sea breezes should lead to shower development over interior and leeward areas this afternoon. Shower coverage will increase over Kauai this evening and over Oahu late tonight.
Overall, predominantly VFR conditions will prevail at most TAF sites during the next 24 hours. Some MVFR cigs will be possible early this morning at PHLI and MVFR/IFR cigs will be possible at PHNY at times today and tonight.
AIRMET Tango remains in effect for moderate upper-level turbulence over the entire state and will likely continue through the day and into tonight. See SIGMETs Tango and Victor series for severe turbulence areas over the islands.

Marine

The pressure gradient is weakening from the high pressure far northeast of the islands in response to the first of two cold front that will approach the local waters from the west. As a result, gentle east winds will transition to light southeast breezes this morning. Winds will become more southwesterly to westerly through the day as the front reaches and passes into the western nearshore waters tonight into Monday morning. This first front will likely reach the northwestern Kauai coastal waters by sunrise Monday move through the smaller island coastal waters through the day. As the front lifts northeast of the offshore waters Monday, areawide light to moderate southwesterlies will strengthen. A potentially deepening surface low northwest of the islands will move north of the island chain through the middle of next week. This will push a second and stronger front across the area Wednesday. Post-frontal west to southwest winds may reach moderate to locally strong Small Craft Advisory (SCA) magnitudes across the majority of the marine zones from as early as Tuesday afternoon. SCA level winds will likely persist through late Wednesday night. Isolated thunderstorms will remain possible over the west or far northern offshore waters through the middle of the week as these fronts move across to the east.
A short duration northwest fetch behind a front skimming the far north offshore waters Monday will push in a small, medium period northwest (310 degree) swell tonight into Monday. This will pick up Kauai, Oahu and Maui's north-facing shore surf by a foot or so tomorrow. A storm advancing to just west of the Dateline along 40N later today will send a small, medium period swell toward the region early this week. This small to medium size swell will be enhanced as this system develops a deepening low northwest of the offshore waters early Wednesday. The generated large, medium period northwest swell (310 degrees) will move through during the day Wednesday. If this swell materializes as model guidance suggests, it will likely produce warning level surf along most north and west-facing shores Wednesday and Thursday. Very small, medium period background south swell, with a small bump expected today along the eastern end of the state, will generally maintain just knee high surf along many south-facing shores. Choppy, more rough surf conditions could develop across the southern nearshore waters during the middle of next week if and when west to southwest winds achieve locally fresh to strong magnitudes (in relation to the mid week frontal passage).East-facing shore surf is steadily declining in direct response to easing trades. This east chop will continue to lower the next couple of days.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov