Issued: Jul 22, 2014 2:30 PM HST
Water vapor imagery shows an upper level trough is centered a few hundred miles to the northwest of Kauai. The trough has been moving slowly northward over the past several hours. Instability associated with the trough is causing some thunderstorms to form near its center and along its eastern periphery just to the north northwest of the state. Some thin high clouds are also streaming up from the south along the troughs eastern periphery mainly moving over Maui county and the Big Island including the adjacent coastal waters.
Cloud coverage over the islands varied from island to island but has increased quite a bit since early this morning. Instability associated with the above mentioned trough combined with daytime heating has caused some isolated towering cumulus and cumulonimbus clouds to form especially over the leeward Big Island slopes. Cloud tops are estimated to be up to around 35000 feet. Over Kauai clouds are covering most eastern and interior areas with scattered low clouds seen elsewhere. Over Oahu low clouds are banked up over the slopes and summits of both the Koolau and Waianae mountain ranges with scattered low clouds seen elsewhere. Over Molokai low clouds are covering east sections with a few patches of low clouds also seen over interior Lanai. Over Maui patches of low clouds are covering the slopes of Haleakala as well as the slopes and summits of the west Maui mountains. Over the Big Island clouds have built up over most of the area with a few breaks seen over the leeward Kohala slopes and over the high summits.
The ITCZ is rather inactive at the present with some isolated thunderstorms along its axis which is generally running along 10°N. Individual thunderstorms are moving along toward the west at around 15 mph.