Issued: May 03, 2011 7:45 PM HST
An area of isolated to scattered cumulonimbus, CB, persists over and just southwest of the main Hawaiian islands, specifically bounded by 22°N 161°W, 19°N 155°W, 17°N 165°W, 22°N 161°W. Some CB tops have temperatures around minus 57 degrees c, corresponding to heights near 38000 feet using the afternoon Lihue sounding. The bulk of this activity lies just outside Hawaii coastal waters. However, radar still shows isolated moderate to heavy showers across some windward areas of the islands.
Water vapor loop shows a northeast to southwest oriented upper trough across the islands, with an axis extending through 28°N 140°W and 18°N 170°W. The CB area lies just east of the upper trough axis. An upper low near 23°N 148°W lies within the upper trough as does a weaker upper low near 21°N 164°W. The southern flank of the upper trough is marked by a ragged 300 mile wide band of broken to overcast high clouds south of a line from 17°N 142°W to 11°N 160°W.
Broken to overcast layered clouds north and west of a line from 44°N 140°W to 37°N 151°W to 37°N 170°W to 35°N 180°W mark a series of fronts moving eastward within the storm track far north of the main Hawaiian islands. A broad anticyclonic circulation is noted in low cloud motion, with a center roughly near 42°N 131°W. This circulation center, actually a center of high pressure, has an associated ridge extending southwest through 33°N 150°W and 30°N 163°W. Since the main Hawaiian islands lie south of this ridge, local prevailing flow is east to west across local Hawaiian waters.
High clouds from nearby CB are blocking the view of lower clouds across Hawaiian leeward waters this evening. An area of broken to overcast layered clouds lies 60 to 240 miles northeast of the islands of Maui county and Oahu, moving toward the southwest at 15 to 20 mph. A single CB near 22°N 155°W, about 100 miles northeast of Maui, lies within this layered cloud area. Scattered to patchy broken low clouds prevail elsewhere across windward waters. Last visible imagery showed patchy broken low clouds across most windward areas of the islands, with towering cumulus noted across leeward Big Island slopes.