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An unseasonably strong cold front will move down the island chain today and tonight, then east of the Big Island on Sunday. The front will be accompanied by a potent deep-layer low that will pass just north of the islands through the weekend. The combination will bring a period of unsettled weather, including the potential for thunderstorms and heavy showers as well as shifting gusty winds.

The gradient between a ridge to the east and the approaching front (now nearing Kauai) will support increasing south to southwest winds in areas east of the front today and tonight, with a shift to gusty northwest to north winds after the front passes. A Small Craft Advisory has been issued for all waters, as sustained southwest to northwest winds will periodically reach the 25 kt criteria, and due to the potential for additional marine hazards for small craft, including wind gusts to 40 kt.

The front is expected to move quickly down the island chain today, reaching Oahu by midday, Maui County in the late afternoon, and the Big Island tonight into Sunday. The post-frontal northwest winds are expected to diminish Sunday night into Monday, when a weak surface low is expected to be northeast of the islands. This will support light to moderate northwest winds that will weaken and become variable Tuesday/Wednesday as the low weakens to a trough.

The current small northwest swell is expected to persist through tonight. A surface low accompanying the front will send a moderate-sized, sloppy, short-period northwest swell toward the islands tonight through Monday, with surf expected to remain below advisory levels as the swell peaks Sunday night. Small short-period northeast swell will persist for the next several days, while a small long-period northwest swell is possible around the middle of next week. Relatively small southwest swells will arrive in the islands through the most of the next week, supporting small surf along exposed south and west facing shores. A more significant south swell is possible by the end of the week.

Hawaii Wave Height Model

Tide Predictions

The sunrise was at 05:51 am this morning and will set at 06:53 pm this evening. The Moon is currently 29 days old, and is in a New Moon phase. The next Waxing Crescent will occur at 7:06 PM on Friday, April 12th.

Maui Weather

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Wind: n/a at 0 mph
Sunrise:
Sunset:
current observations as of 12pm June 18th, 2019

Weather Outlook for Saturday, 4th May 2019

Summary

An out of season cold front nearing Kauai early this morning will continue eastward down the island chain today and tonight. Instability associated this front and a potent upper low dropping south toward the islands along with plenty of moisture will bring a period of heavy showers, gusty winds, and possibly a few strong thunderstorms. Drier and cooler northwest winds will fill in behind the front tonight through Monday, with trade winds unlikely to make a return until Thursday.

Detailed Discussion

Water vapor imagery showed an anomalously potent upper low dropping south toward the islands this morning (associated cold pool around -20 C aloft). At the surface, the attendant cold front is quickly moving toward Kauai and will approach Oahu through the morning hours today. Isentropic lift combined with plenty of moisture (dewpoints in the upper 60s; above normal PWs) to work with out ahead of this boundary and upper low continue to trigger moderate to heavy showers from Kauai to Maui County. As the morning progresses and the forcing for ascent and instability increase, conditions will continue to deteriorate over the smaller islands. The latest hi-res model reflectivities remain in good agreement and show the main line of showers along and ahead of the front continuing eastward over the Kauai Channel and Oahu from daybreak through noon, then toward Maui County through the afternoon hours. The potential for localized flooding and a few strong storms with rotating updrafts (0-6 km effective bulk shear values up to 35 to 45 knots) will remain a possibility over these areas today. Additionally, strong straight-line winds up to 40 mph can’t be ruled out in and around any heavy showers or storms that materialize. Barking Sands on Kauai has already recorded wind gusts up to 35 mph due to heavy showers moving ashore earlier.

The front will continue eastward across the eastern end of the island chain tonight into Sunday. Although some weakening will be a possibility through this time, the potential for heavy showers, gusty winds and strong storms will remain in the forecast. The upper low is forecast to drop south to an area just north of the islands through this time, then slowly shift east-northeastward and away from the area Sunday through Monday. A secondary vort lobe wrapping around the back-end of this upper feature will likely translate to a band of clouds and showers moving through from west to east late tonight into Sunday.

Very cool conditions, by May standards, are expected to fill in on the northwesterly flow late tonight through Monday. The latest guidance drops dew points into the upper 50s, and daytime high temperatures will likely remain in the upper 70s, which is highly unusual for early May.

There is no real sign of trade winds until Thursday. As the upper level low fills and lifts off to the northeast Tuesday and Wednesday, it will leave a weak area of low pressure north of the state. This will produce generally weak west to northwest winds over the islands and will likely lead to somewhat dry conditions.

Central Valley (Kahului, Spreckelsville):

Cloudy. Occasional showers and slight chance of thunderstorms in the evening, then showers likely after midnight. Locally heavy rainfall possible. Lows around 66. South winds up to 10 mph. Chance of rain 80 percent.

Leeward West (Lahaina, Ka`anapali):

Mostly cloudy. Occasional showers and slight chance of thunderstorms in the evening, then showers likely after midnight. Locally heavy rainfall possible. Lows around 67. West winds 10 to 15 mph. Chance of rain 80 percent.

Windward West (Wailuku, Waiehu):

Mostly cloudy. Occasional showers and slight chance of thunderstorms in the evening, then showers likely after midnight. Locally heavy rainfall possible. Lows 57 to 68. West winds up to 15 mph. Chance of rain 80 percent.

Windard Haleakala (Hana, Haiku, Makawao):

Mostly cloudy. Breezy. Showers likely and slight chance of thunderstorms in the evening, then showers likely after midnight. Locally heavy rainfall possible. Lows around 67 at the shore to around 52 at 5000 feet. Southwest winds up to 20 mph. Gusts up to 45 mph after midnight. Chance of rain 70 percent.

Leeward Haleakala (Kihei, Wailea, Makena):

Cloudy and breezy. Occasional showers and slight chance of thunderstorms in the evening, then occasional showers after midnight. Locally heavy rainfall possible. Lows around 67 at the shore to around 55 upcountry. West winds up to 25 mph. Chance of rain 90 percent.

Haleakala Summit

WIND ADVISORY IN EFFECT FROM 8 AM THIS MORNING TO 6 PM HST SUNDAY. Mostly sunny early in the morning then becoming partly sunny. Very windy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Slight chance of thunderstorms late in the afternoon. Locally heavy rainfall possible late in the afternoon. Highs around 55 at the visitor center to around 52 at the summit. Southwest winds 20 to 45 mph. Chance of rain 50 percent.