West Side

Tonight: Partly cloudy. Isolated showers after midnight. Lows 64 to 73. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny with isolated showers. Highs 73 to 86. East winds up to 20 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

Tuesday Night: Breezy. Partly cloudy with isolated showers. Lows 63 to 72. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

South Side

Tonight: Mostly clear. Lows 65 to 70. North winds up to 15 mph.

Tuesday: Sunny and breezy. Highs 76 to 87. North winds up to 20 mph shifting to the northeast 10 to 20 mph in the afternoon.

Tuesday Night: Mostly clear. Lows around 68. Northeast winds up to 15 mph.

North Shore

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 67 to 72 near the shore to around 53 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 78 to 83 near the shore to around 66 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 70 near the shore to around 53 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Central Maui

Tonight: Mostly clear. Breezy. Scattered showers late in the night. Lows 65 to 70. East winds up to 20 mph decreasing to up to 10 mph after midnight. Chance of rain 40 percent.

Tuesday: Mostly sunny. Breezy. Scattered showers in the morning. Highs 80 to 87. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Tuesday Night: Partly cloudy. Breezy. Lows 65 to 70. Northeast winds up to 20 mph.

Upcountry

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows around 43 at the visitor center to around 40 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny with scattered showers. Highs 51 to 68. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 43 at the visitor center to around 40 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

East Maui

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 67 to 72 near the shore to around 53 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 78 to 83 near the shore to around 66 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 70 near the shore to around 53 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Lanai City

Tonight: Mostly clear. Lows 59 to 66. Northeast winds up to 15 mph.

Tuesday: Mostly sunny. Breezy. Highs 68 to 79. Northeast winds up to 20 mph increasing to 15 to 25 mph in the afternoon.

Tuesday Night: Mostly clear. Breezy. Lows 58 to 66. Northeast winds 10 to 20 mph.

Kaunakakai

Tonight: Partly cloudy. Isolated showers until early morning. Lows 55 to 73. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 67 to 86. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday Night: Breezy. Mostly clear with isolated showers. Lows 55 to 72. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to breezy trades will deliver clouds and showers to windward and mauka areas through the week. Trades strengthen slightly beginning Thursday.

Discussion

The weak upper low that has lingered around the area during the last week is presently positioned northeast of the Big Island at 250mb and roughly over/immediately east of the island at 500mb where the center is analyzed at 583dm. The islands reside along the southern periphery of the attendant cold pool and observed 500mb temperatures are approximately -9C and -10C at Lihue and Hilo respectively as of 12 UTC this morning. This low will sag southeast and tend to deepen as the mid-latitude pattern eases southward during the next couple of days. At the same time, energy associated with a progressive mid- latitude trough will pinch off from the westerlies as it crosses 160W and close off in the vicinity of Kauai during Wednesday. The islands, residing between these two rather small scale lows, will be positioned below a narrow band of shortwave ridging aloft Wednesday into Thursday. Attendant height rises in the mid-levels may nonetheless be hard to come by as the overall geopotential height field remains depressed and even further deepens given that the weak low presently over/east of the Big Island is modeled to deepen to 579dm as it drifts eastward. As a consequence, little change in the thermodynamic profile is anticipated today into Thursday with the exception of the aforementioned upper-level ridging helping to quash afternoon thunder potential over the Big Island. Moderate to locally breezy trades will remain weakly stable during this time with pockets of heavier showers developing where low-level convergence is maximized, mainly Leeward Big Island along the sea breeze each afternoon. Here, nuisance flooding is not out of the question.
By Thursday, lapse rates steepen to 6.5 to 7.0C/km over the western end of the state, the GFS being notably colder and unstable aloft compared to the EC which settles the low further west. Regardless of the model differences, ridge amplification east of the Dateline will cause trades to strengthen during this time limiting the potential for areas of enhanced convergence to emerge anywhere except Leeward Big Island. As a result, expect some variety of moderately unstable trades to develop no later than Thursday and continue through at least Friday night. From a sensible weather perspective, this suggests quick-moving/transient trade wind showers some of which may be heavy, especially at night and during the morning. The potential for thunderstorms over leeward/interior portions of the Big Island on Thurs/Fri will be evaluated going forward as this area stands the greatest chance to experience organized heavy rainfall as diurnal convection develops each afternoon.

Aviation

Trade winds will return to a more easterly direction tonight and strengthen into the moderate to locally breezy range from Tuesday onward as the ridge builds in north of the state. Expect passing showers mainly over windward and mountain areas and along leeward convergence cloud bands through Tuesday, with brief MVFR conditions possible within any shower bands. No AIRMETs are currently in effect.

Marine

Trades will persist through the weekend, with the strongest winds expected late Wednesday and Thursday. Currently, a 1032 mb centered nearly 1400 nm northeast of the state is driving moderate to fresh trade winds. Surface low pressure will form far north of the islands tonight and push the surface high eastward on Tuesday. Meanwhile, another area of high pressure from the west Pacific will move into the central Pacific, then stall far north of Hawaii on Wednesday into Friday. As the new high moves in, expect trade winds to increase to fresh to strong levels on Wednesday or Thursday, when a Small Craft Advisory (SCA) will be needed for the typically windy waters around the Big Island and Maui. The high is forecast to retreat westward during the weekend, favoring a decrease in winds.
Surf along south facing shores will remain just below seasonal average into Saturday as pulses of south-southwest and southwest swell move through. Surf will decline Sunday and remain small into early next week.
East shore surf will remain near or just below seasonal average during the next couple of days, followed by a slight increase Thursday and Friday as trade winds build east of the islands. A gradual decline in east shore surf is expected during the weekend and early next week. Tiny surf will prevail along north facing shores this week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov