Last Updated on Wednesday, 22 May 2013 23:50
Issued: May 23, 2013 8:30 AM HST
High pressure is driving a trade wind flow over the eastern portion of the central north Pacific while troughing continues to exert a greater influence over the western and central portions. The main Hawaiian islands lie under a transition between these features, with trades winds slowly building over the eastern end of the state.
Weakening surface troughs lingering north of the main Hawaiian islands are holding off the rebuilding trade flow. One trough is drifting westward along 157°W from just north of west Maui to 30°N. Scattered to broken cumulus clouds extend about 275 miles east of the trough axis. Another, weaker surface trough sits about 475 miles northwest of Kauai from 29°N 162°W to 25°N 170°W. These surface troughs are supported by a nearly stationary upper level trough overhead running along 30°N 156°W to a weak embedded upper low at 23°N 170°W to another embedded upper low at 14°N 178°W.
Over the islands, overnight land breezes dominate from the Big Island to Oahu due to the sluggishness of the returning trade winds. Mainly scattered cumulus around these islands are travelling from the east at 10 mph, increasing to slightly more than 15 mph south of the Big Island. As a result, patches of broken low clouds are observed along windward slopes while leeward areas are mostly clear. To the east of the state, especially east of 150°W, a rather stable trade wind flow is well established. The surface high driving the trades is centered north of the area near 40°N 142°W.
The upper trough to the west is generating a broad area of broken midlevel clouds over Kauai and waters to the west. An embedded line of towering cumulus clouds with tops to 19000 ft is moving to the north northwest slowly just south of Kauai and Niihau.
Over the western portion of the area, a weak cold front is approaching Midway atoll from the west. The exact location and movement of the front is difficult to determine as waters within 200 miles northwest and southeast of Midway are obscured by broken layered clouds.