Hurricane Iselle weakens to a Tropical Storm as it nears Hawai’i

August 8th, 2014 |
Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 23:47 UTC on 07 August 2014 (above) showed Category 1 Hurricane Iselle just east of Hawai’i, exhibiting a convective burst within the northern semicircle and cloud-top IR brightness temperatures as cold as -82º C. With the approach of Iselle, the Central Pacific Hurricane Center issued its first Hurricane Warning for a portion of Hawaii since 1993.

An animation of GOES-15 0.63 µm visible channel images during daylight and 10.7 µm IR images at night (below; click to play animation; also available as an MP4 movie file) revealed a deteriorating satellite signature as the hurricane approached the Big Island of Hawai’i — and Iselle was downgraded to a Tropical Storm around 08 UTC on 08 August. However, abundant moisture and orographic effects led to some locations receiving over 10 inches of rainfall in a 24-hour period. In fact, one final convective burst could be seen developing after about 11:00 UTC, moving over the southeastern portion of the Big Island after about 12:45 UTC.

GOES-15 0.63 µm visible channel and 10.7 µm IR channel images [click to play animation]

GOES-15 0.63 µm visible channel and 10.7 µm IR channel images [click to play animation]

The period of deteriorating satellite signature and weakening intensification were due to the storm encountering increasing deep layer wind shear (below).

GOES-15 10.7 µm IR channel images with an overlay of deep layer wind shear

GOES-15 10.7 µm IR channel images with an overlay of deep layer wind shear

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