Mesovortices within the eye of Hurricane Lowell

August 21st, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (above; click image to play animation; also available as an MP4 movie file) revealed the presence of mesovortices within the eye of Category 1 Hurricane Lowell in the East Pacific Ocean on 21 August 2014.

The mesovortices were also evident at 21:07 UTC in a Suomi NPP VIIRS true-color image from the SSEC RealEarth web map server (below).

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

In addition to having a rather large eye, Hurricane Lowell also had a large radius of strong winds, as seen on a comparison of a GOES-15 0.63 µm visible image and Metop ASCAT surface scatterometer winds from the CIMSS Tropical Cyclones site (below).

GOES-15 0.63 µm visible channel image with Metop ASCAT surface scatterometer winds

GOES-15 0.63 µm visible channel image with Metop ASCAT surface scatterometer winds

GOES-14 SRSOR: Tropical Storm Lowell in the East Pacific Ocean

August 19th, 2014
GOES-14 0.63 µm visible channel images (click to play Animated GIF)

GOES-14 0.63 µm visible channel images (click to play Animated GIF)

The GOES-14 satellite was in Super Rapid Scan Operations for GOES-R (SRSOR) mode, providing coverage of Tropical Storm Lowell in the East Pacific Ocean on 19 August 2014; an animation of 0.63 µm visible channel images (Animated GIF | MP4 movie file | YouTube) showed a gradual increase in the organization of a convective banding structure during the day. At 12 UTC Tropical Storm Lowell was located several hundred miles southwest of Baja California, with a center at 15.5º North latitude, 119.5º West longitude.

GOES-15 10.7 µm IR channel images with an overlay of Metop ASCAT surface scatterometer winds from the CIMSS Tropical Cyclones site (below) showed the the strongest winds (40.0-49.9 knots, yellow barbs) were in the southeastern quadrant of Lowell at 17:11 UTC.

GOES-15 10.7 µm IR images with Metop ASCAT surface scatterometer winds

GOES-15 10.7 µm IR images with Metop ASCAT surface scatterometer winds

A comparison of the 16 UTC GOES-15 10.7 µm IR channel image with the corresponding DMSP SSMIS 85 GHz microwave image (below) indicated that the highest rainfall rates were associated with the convective banding  (and coldest cloud tops) within the southern semicircle of the storm.

GOES-15 10.7 µm IR image and DMSP SSMIS 85 GHz microwave image

GOES-15 10.7 µm IR image and DMSP SSMIS 85 GHz microwave image

Stratospheric intrusion vortices over the East Pacific Ocean

August 8th, 2014
GOES-15 6.5 µm water vapor channel images (click to play animation)

GOES-15 6.5 µm water vapor channel images (click to play animation)

GOES-15 6.5 µm water vapor channel images (above; click image to play animation; also available as an MP4 movie file) showed the development of a train of stratospheric intrusion vortices over the East Pacific Ocean during the 07 August – 08 August 2014 period. These vortices formed along a middle to upper tropospheric wind shear axis, and propagated toward the northeast.

The corresponding GOES sounder Total Column Ozone product (below; click image to play animation) revealed ozone values as high as 375 Dobson Units (lighter green color enhancement) within the more well-defined stratospheric intrusion vortices, due to the fact that ozone-rich stratospheric air was descending as the tropopause heights were lowered within the cyclonic vortex circulations.

GOES sounder Total Column Ozone product (click to play animation)

GOES sounder Total Column Ozone product (click to play animation)

Other examples of stratospheric intrusion vortices can be found here, here, here, and here.

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