Based on data through 0000 UTC October 20 2010.

There has been a big increase in cloud cover over the main Hawaiian islands since this morning.

Overcast clouds cover most of the Big Island, extending upslope near the summits of Mauna Kea and Mauna Loa. Clouds remain scattered only along the coast and lower slopes from Keahole Point to Upolu Point.radars have been showing locally heavy showers over the southeast slopes of the Big Island between Volcano and Pahala. Broken to overcast clouds also cover most of east Maui. Radars show isolated heavy showers near makena. The weather is les active from Kahului northwestward. Clouds remain scattered over most areas from central Maui to Kauai but there are patchy broken low clouds over the northeast slopes of the west Maui mountains, over the south slopes of Lanai, over the mountains of east Molokai, over both the Koolau and Waianae mountains of Oahu and over the southwest slopes of Kauai. Clouds are isolated over Niihau.

Low clouds around the main Hawaiian islands are moving from the northeast around 10 mph, from a more northerly direction than the typical trade-wind flow. Clouds are very isolated over water around the islands from niiahu to Lanai. A 35 mile wide line of broken low clouds extends 335 miles northeast from over east Maui. Broken to overcast layered clouds extend 90 nm NE of the Big Island. Isolated cumulonimbus clouds, cb, have been popping up just offshore of windward Hawaii.

A 50 to 150 mile wide frontal cloud band lies north of a line from 28.5°N 150°W to 225 miles north of Kauai to 25°N 165°W to 30°N 177°W. The part of the band northeast of 28°N 154°W contains deep overcast layered clouds and isolated cumulonimbus clouds, cb, with tops to 35000 ft. The cb have become less active than they were this morning. The part of the band west of 154°W contains showery broken to overcast low clouds. Over the past 6 hours the part of the frontal band east of 165°W has been moving toward the southeast at 10 mph while the part west of 165°W has been nearly stationary. A series of small vortices has formed along the band since this morning and the band is starting to fragment. One vortex is near 30°N 152°W, one is about 300 miles north of Kauai near 26°N 159°W, and one is near 31°N 180°W.

A 500 mile wide area of broken to overcast layered clouds and isolated embedded cb is southeast of a line from 30°N 149°W, 400 miles east of Hilo to 10°N 155°W. Most of the cb are southeast of a line from 10°N 150°W to 15°N 145°W. Over the past several hours this area has shifted east slowly. In the past few hours the cb north of 15°N have decreased, while those south of 15°N have intensified.

Water vapor imagery, which shows features mainly above 24000 ft, shows a trough aloft from 25°N 146°W over the Big Island to 19°N 160°W to 19°N 180°W. The part of the trough near the islands has been moving toward the southeast at 10 mph. Another trough aloft is centered from 30°N 152°W to 25°N 156°W. The second trough has been moving toward the east southeast at 35 mph.