Thursday, April 24, 2014 596-SURF , 596-WAVE , 922-BONG , 638-RUSH , 572-SURF(MAUI) , 241-SURF (KAUAI) , 324-RUSH (BIG ISLAND)
   
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2.3.14 9am. On 4/22
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Winds Statewide in a glance ...just go HERE(this link is also the 4th drop down under weather)

Apr 23, 2014 4:00 AM HST

Synopsis
Strong ridging north of the state will maintain breezy and gusty trade winds through Saturday. Low clouds and showers carried by the trades will remain focused mainly along windward facing slopes of the island chain, but some brief showers will continue to be blown over to leeward sections of the smaller islands, especially during nights and mornings. A slight increase in showers is expected across parts of the state late Thursday. The trade wind speeds are forecast to gradually decline from Sunday into early next week.

Discussion
A 1028 mb surface high centered near 32°N 142°W, or more than 1250 miles northeast of Honolulu, is moving toward the southeast at about 10 mph. A surface ridge extends west from this high through a point about 650 miles north of Honolulu. The relatively tight pressure gradient south of these features continues to maintain breezy and locally gusty trade winds across the main Hawaiian islands early this morning.

Aloft, the close proximity of a strong mid-tropospheric anticyclone northeast of the islands is maintaining stable atmospheric conditions across the region tonight. As a result, the low-level trade wind inversion is around 6 thousand feet. This relatively low inversion height has contributed to maintaining the gusty trade winds across parts of the state tonight. This is especially true in valleys downwind of higher terrain, such as the Koolau mountain range on Oahu. Satellite imagery and radar reflectivity data also show limited shower bearing clouds over and immediately upstream of the state. Therefore, the stable conditions due to the mid-tropospheric anticyclone are likely contributing to the reduction of rainfall over most of the region. Note that the presence of an upper tropospheric trough near Kauai continues to send patches of cirrus up over parts of the island chain this morning.

The forecast models indicate strong surface ridging will continue north of the islands between latitudes 30°N and 35°N into Saturday. The tight pressure gradient south of this ridging will keep the trade winds breezy and gusty. Also, the strong mid-tropospheric ridging over the region will maintain stable atmospheric conditions through the end of the work week. At the same time, the low-level trade wind inversion will cause periods of enhanced wind gusts over and downwind of higher terrain across parts of the state. In fact, the GFS and ECMWF models suggest there may be another increase in 850 mb winds by late Thursday at the same time a new surface high passes north of the state. This could lead to another round of strong trade winds, which may require the issuance of wind advisories for parts of the state.

The forecast guidance indicates we should continue to have a rather typical trade wind weather pattern with low clouds and showers mainly affecting windward facing slopes. However, the remnant moisture from a decaying front east northeast of the state will likely ride in on the increasing low-level trade wind flow by late Thursday. As a result, a slight increase in precipitation over windward and mauka areas Thursday, especially Thursday night. At the same time, the strengthening trade winds may carry some brief showers over to leeward sections of some of the smaller islands, especially during Thursday night and early Friday morning. Besides the potentially wetter conditions late Thursday, the forecast guidance does not show any other organized system with enhanced coverage of showers moving into the area through this weekend.

The upper level trough is forecast to continue to weaken and lift out to the northeast later today and tonight, which is expected to diminish the coverage of cirrus clouds near the islands. However, a new upper level trough moving into the vicinity of the main Hawaiian island chain this weekend may produce widespread high clouds over parts of the state again starting Saturday.

The longer range forecast models indicate the trade wind speeds will begin to decrease from late this weekend into early next week as the surface ridge to the north of the area weakens. Note that recent runs of the ECMWF model weaken the winds more than the most recent runs of the GFS model. The current forecast is a blend of these models, so there may be some adjustment up or down to the trade wind speeds early next week once the models start to come into better agreement in the next few days.

The trade wind weather pattern is expected to continue from Sunday into early next week, with mainly windward and mauka showers. However, a weakening frontal band may move southward and reach the state next week. Based on the latest guidance, this feature may enhance rainfall across many areas of the state starting late Tuesday or Wednesday of next week.

Marine
The fresh to locally strong trade winds continue to require a small craft advisory /sca/ remain in effect for all Hawaiian channels and the typically windy waters adjacent to the Big Island and Maui. Since the trade winds will likely remain strong through the remainder of the work week, the SCA is currently in'effect for these waters through Friday. Note that there may be a slight increase in winds by late Thursday thursday, so additional Hawaiian waters may need to be added to the SCA from Thursday night into Friday. The forecast guidance suggests there may be a slow decreasing trend in winds from late Saturday into early next week, so the SCA may eventually be dropped for most or all Hawaiian waters by Sunday or Monday.

The rough elevated surf continues just below the high surf advisory threshold along east facing shores. The most recent observations from the coastal buoys near windward shorelines of the islands have been showing significant wave heights of 7 to 8 feet with a period 8 to 9 seconds. The Wave Watch III model guidance suggests there will be little variation in these wave heights and periods into Saturday. Surf heights are expected to gradually diminish along east facing shores from Saturday night through Monday.

Elsewhere, the new long-period northwest swell has arrived at buoy 51101 northwest of Kauai. Forerunners fromm this new swell have also arrived at the Hanalei buoy near the north shore of Kauai. This swell will gradually build across exposed north and west facing shores of the islands today, and peak on Thursday. The Wave Watch III model indicates surf produced by this swell will remain below the high surf advisory criteria along north and west facing shores of the smaller islands. However, we will monitor the buoy observations in case the swell is larger than forecast. This northwest swell will gradually subside from Friday through Saturday. No other significant swells are expected through next Tuesday.

Watches/Warnings/Advisories
Small craft advisory until 6 pm HST Friday for all Hawaiian channels, Maalaea Bay and the waters south of the Big Island.

 

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