West Side

Today: Sunny and breezy. Highs 78 to 89. East winds up to 15 mph shifting to the northeast in the afternoon.

Tonight: Partly cloudy. Lows 68 to 75. Northeast winds 10 to 15 mph.

Monday: Mostly sunny. Isolated showers in the morning. Highs 77 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Side

Today: Sunny. Highs 78 to 90. North winds up to 15 mph shifting to the northeast in the afternoon.

Tonight: Mostly clear. Lows 69 to 77. Northeast winds 10 to 15 mph.

Monday: Sunny. Highs 78 to 90. North winds 10 to 15 mph.

North Shore

Today: Mostly sunny with isolated showers. Highs 81 to 87 near the shore to around 69 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 73 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 86 near the shore to around 69 near 5000 feet. East winds 10 to 15 mph. Chance of rain 30 percent.

Central Maui

Today: Sunny and breezy. Highs 82 to 90. Northeast winds 10 to 20 mph.

Tonight: Mostly clear. Lows 68 to 73. East winds around 10 mph.

Monday: Sunny. Isolated showers in the morning. Highs 82 to 89. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Sunny with isolated showers. Highs around 65 at the visitor center to around 67 at the summit. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 46 to 55. East winds 10 to 15 mph. Chance of rain 20 percent.

Monday: Sunny with isolated showers. Highs around 64 at the visitor center to around 66 at the summit. East winds 10 to 15 mph. Chance of rain 20 percent.

East Maui

Today: Mostly sunny with isolated showers. Highs 81 to 87 near the shore to around 69 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 73 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 86 near the shore to around 69 near 5000 feet. East winds 10 to 15 mph. Chance of rain 30 percent.

Lanai City

Today: Sunny. Highs 73 to 83. Northeast winds up to 15 mph.

Tonight: Mostly clear. Lows 64 to 69. Northeast winds around 10 mph.

Monday: Mostly sunny. Highs 72 to 82. East winds up to 15 mph.

Kaunakakai

Today: Sunny and breezy. Highs 73 to 90. Northeast winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Lows 60 to 75. East winds 10 to 20 mph.

Monday: Mostly sunny. Breezy. Isolated showers in the morning. Highs 73 to 91. East winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A high pressure ridge north of the Hawaiian Islands and a weak low drifting westward just southeast of the island chain will boost trade winds slightly through Monday. A high pressure ridge aloft will continue to produce stable subsident conditions across the region with limited shower activity lasting through Monday. Weather conditions shift towards the wetter side on Tuesday and Wednesday as a wave moving through the low level easterlies increases clouds and showers as the trough passes westward across the state. Additional instability will develop over the islands from Thursday into next weekend, increasing clouds, showers and humidity levels a bit.

Discussion

Looking at the large scale weather pattern we see a high pressure ridge anchored just north of the Hawaiian Islands and a weak low pressure system drifting westward just southeast of the state. Increasing pressure gradients from these two systems will boost wind speeds slightly through Monday as compared to Saturday. Dry summer weather conditions with moderate to locally breezy trade winds will continue with little changes to the overall pattern through Monday.
The pattern begins to weave towards the wet side on Tuesday as a weak wave drifting westward through the low level easterlies increases clouds and showers across the islands. This trough appears a bit weaker than the last low level easterly wave that brought a decent amount of rain to the islands a few days ago. This means we are forecasting lower rainfall amounts with increasing rainfall coverage favoring the overnight to early morning hours. While windward and mountain areas will see the majority of enhanced shower activity during this time period, some of the stronger trade wind showers will drift into the leeward areas west of island mountains.
Unsettled weather conditions will likely continue from Thursday into next weekend as a combination of deep easterlies up to around 18,000 feet will interact with subtropical jet stream divergence to enhance typical trade wind showers over all islands. Long range weather model solutions are suggesting the subsidence temperature inversion heights will hover around the 7,000 foot elevation level, which supports isolated to scattered showers during the day, and scattered to numerous showers at night with windward mountain areas seeing the higher coverages in this range. Day to day changes in the forecast shower pattern for each island remains likely this far out, and thunderstorms over the western higher elevation slopes of the Big Island cannot be ruled out during this time period. Stay tuned.

Aviation

A high pressure ridge north of the islands and a weak low southeast of the Big Island will keep moderate to breezy easterly trade winds in the forecast through Monday. Stable conditions aloft will keep clouds and showers to a minimum with windward airfields seeing brief periods of shower activity.
No AIRMETs are in effect. An AIRMET for moderate low level turbulence over and south through west of island mountains may be needed later today due to increasing winds.

Marine

Weak surface high pressure will remain nearly stationary north of the islands today. A low slowly moving west southeast of the state will create a tight enough pressure gradient across the nearshore waters to result in another couple of days of moderate to locally strong trades. The Small Craft Advisory (SCA) has been extended for the windier waters surrounding Maui County and Big Island through Monday afternoon. A cold front passing atop this high north of the state will slightly weaken it before the backing high behind the front re-tightens the downstream pressure gradient. However, the weakening low drifting westward just south of the islands will keep trade winds at similar speeds through Monday. Expect a brief drop off in wind speeds by Tuesday, with trades picking back up to more fresh to locally strong magnitudes by Wednesday.
The recent small, medium period north swell will significantly fall off today and produce waist high surf by late afternoon. Another medium period north swell arrival Thursday may cause a slight bump in late week surf along north-facing shores. Surf along south-facing shores will remain near or slightly above late summer norms today. A small, longer period south swell reinforcement arriving early this morning will hold today's south shore surf to around waist high. Typical east-facing shore short period wind wave chop will hold through Monday as the islands remain under a moderate trade fetch over and just upstream of the islands.

Fire weather

Low humidity levels will continue today with sustained wind speeds approaching critical fire weather thresholds for a few hours each afternoon through Monday. Expect decreasing fire weather threats from Tuesday into next weekend due to higher afternoon minimum humidity levels. Temperature inversion heights near the Big Island and Maui will range from 5,000 to 6,500 feet today.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov