Area Forecast Discussion for Hawaii

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Issued: Jul 25, 2014 3:30 AM HST

The trade winds will become moderate today and Saturday. Windward showers will continue through the next several days, mainly at night and during the morning hours. A slight increase in shower activity is expected during the weekend, with trades regaining strength late Sunday and into early next week.

The strong sfc high pressure located far NNE of the main Hawaiian islands will relax a little today as a weak trough passes just to the N of the island chain and continues to migrate E through the weekend. This will bring a weakening of the trades during the next couple of days. Showers are still favoring windward and mauka, but latest radar data show a significant reduction in shower/rainfall coverage across the islands compared to previous nights. Mimic and model moisture analyses depict a dryer airmass upstream of the islands, with pwats steadily decreasing to around 1 to 1.3 inches. 12Z soundings depict strong inversions around 6 thousand feet, which should make vertical development of showers rather difficult. A mid/upper level high just SW of the islands is also supporting an associated ridge, which is extending through the island chain. This synoptic setup should result in relatively benign weather conditions across the aloha state at least through early Saturday.

Meanwhile, models show an area of enhanced tropical moisture gradually approaching the main Hawaiian islands and possibly bringing a slight increase in showers by late Sat. Also, a low pressure system will pass far S of the aloha state heading W which could tighten pressure gradients across the islands. This may bring increasing trades late in the weekend and into early next week.

By the middle of next week, models show potential for yet another surge of tropical moisture approaching the aloha state from the SE, around the wed/thu timeframe. This moisture will help in significantly enhancing trade wind showers across the island chain once more.

Vfr conditions will dominate over most areas today. Windward slopes will see isol MVFR cigs as small pockets of moisture ride in on the trade wind flow. Radar VAD wind profiles show that low level winds are down slightly in the 15 to 20 kt range. As a result, airmet tango for low level turb will likely be cancelled before sunrise.

The small craft advisory for for the typically windier waters around the Big Island and Maui has been cancelled. Winds are expected to again increase late Sunday and into early next week as a developing system passing well south of the state helps to tighten the pressure gradient.

No significant swells are expected through the next several days. Small long-period background swell from the SSW and short-period swell from the SE represent the swell sources from the southern hemisphere, while short period wind waves from the east represent the only source of swell from the northern hemisphere.