West Side

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 86. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 76. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs 82 to 87. East winds up to 15 mph. Chance of rain 20 percent.

South Side

Today: Mostly sunny with isolated showers. Highs around 89. North winds up to 10 mph in the morning becoming light. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 70 to 77. North winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Sunday: Sunny. Highs around 90. Light winds becoming north up to 15 mph in the afternoon.

North Shore

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 86 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 73 near the shore to around 54 near 5000 feet. East winds up to 20 mph shifting to the southeast 10 to 15 mph after midnight. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 80 to 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Central Maui

Today: Mostly sunny with isolated showers. Highs 83 to 90. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 72. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

Sunday: Sunny. Isolated showers in the morning. Highs 83 to 90. East winds up to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny with scattered showers. Highs around 63 at the visitor center to around 67 at the summit. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 50 at the visitor center to around 45 at the summit. Southeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Sunny with scattered showers. Highs around 64 at the visitor center to around 68 at the summit. East winds up to 10 mph. Chance of rain 50 percent.

East Maui

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 86 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 73 near the shore to around 54 near 5000 feet. East winds up to 20 mph shifting to the southeast 10 to 15 mph after midnight. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 80 to 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Lanai City

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 82. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows 64 to 69. East winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Sunday: Sunny. Isolated showers in the afternoon. Highs 74 to 82. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 73 to 90. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 62 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Sunny. Highs 73 to 90. East winds 10 to 15 mph.

Detailed Forecast

Synopsis

Lessened stability from a weak upper low northwest of Kauai, along with higher moisture pooling over and north of the islands, will increase statewide shower frequency and coverage. There are moderate chances for periods of heavy rain across the western end of the state with low probabilities for isolated storms over the north nearshore waters. Stable, drier weather is expected to return early next week where trade showers will favor windward exposures and upslope mauka.

Discussion

The wetter pattern commenced overnight as a more moist air mass moved in from the east. It has been a fairly wet early Saturday for Oahu and Maui where many sites have picked up a quick quarter to over an inch of rain the past six hours. Windward mauka are registering higher amounts where some upslope gauges have measured near an inch and a half since late last night. This wet pattern will persist into Sunday as an upper low northwest of the state and associated mid level trough passes through and taps into a more moisture-rich air mass. Both 12Z soundings came in at 1.47 inch pwats or near the 75% climate percentile for mid to late July. Upper air soundings also depict the erosion of the low level temperature inversion in response to the decreasing stability. The westward passing 700 mb trough axis and cooling initiated by lowering heights to the northwest will maintain a deeper, more moist boundary layer.
Stability will continue to erode through the day as a result of the evolution of the northwest upper low in tandem with the passing mid level trough moving in from the east. These features have and will provide a boost in rainfall with the highest rain falling along windward exposures and adjacent nearshore waters. The majority of the GFS and EC ensemble guidance QPF members still depict a distinct swath of higher rain falling between 20 to 25 N. The forcing of the weak low across the far northern maritime will focus better organized convection over the far northern offshore waters into early next week. While confidence is moderately high that more western islands will experience a wetter weekend, the chance for thunderstorms remains relatively low. Upper levels should cool enough to provide the needed instability required to place isolated storms in the proximity of northern Kauai and surrounding waters later today through early Monday. The timing of the heaviest rain will depend upon the evolution of the upper low in conjunction with the greatest pooling moisture.
A stable summer-like trade wind pattern will return by late Monday as lingering moisture advances west and drier air filters into its wake. The upper level low will no longer be an issue from Tuesday onward as it meanders off to the northwest and ridging re-establishes itself over the islands. A northern weak mid level shortwave trough may brush the western end of the state Wednesday. This feature may briefly enhance trade wind showers across the western half of the state. In closing out the week, model guidance does hint of a trough approaching from the east that would briefly disrupt trade flow…weakening winds as they back a touch more northeast.

Aviation

High pressure far to the north will drive moderate to locally fresh trade winds across the state. An area of cloud and showers is expected to continue from the east later today and will likely bring periods of MVFR conditions along windward slopes.
AIRMET Tango is in effect for tempo moderate turbulence below 070 across all leeward areas. This AIRMET may be able to be dropped later this morning as winds weaken slightly. AIRMET Sierra is also in effect for mountain obscuration over the N through E sections of all islands through the morning hours.

Marine

High pressure will remain nearly stationary far northeast of the state through the middle of next week. A weak low-level trough is expected to move through the state from the east through Sunday, weakening the trade winds. The Small Craft Advisory (SCA) for the windier waters and channels around Maui County and the Big Island has dropped this morning and will continue to gradually decline to gentle to locally fresh through the forecast period.
A mixed southerly swell will provide average surf along south facing shores through the morning. The new small long period southwest swell has begun to slowly fill in with long period forerunners showing up on the nearshore buoys early this morning and is expected to continue to fill in through the afternoon, peak late tonight then decline slowly through early next week.
Surf along east facing shores will gradually decline over the weekend with the weakening trade winds. Surf along north facing shores will remain nearly flat through the forecast period.
Peak high tides associated with the lunar cycle could lead to minor coastal flooding along shorelines and low-lying coastal areas next week Monday through Wednesday during the daily peak tide each afternoon.

Fire weather

Fire weather concerns will be low this weekend as a result of a more wet pattern. Trade winds will remain light to locally breezy the next several days with a higher frequency of showers. Drier weather is expected to return early next week. This may increase the fire weather threat over those leeward areas that may not receive the full benefit of significant weekend rain.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov