Tropical Storm Danny in the eastern Atlantic Ocean

August 19th, 2015 |

GOES-13 10.7 µm IR images [click to play animated GIF]

GOES-13 10.7 µm IR images [click to play animated GIF]

The first tropical storm of the season in the eastern Atlantic (Ana, Bill and Claudette all formed over the western Atlantic) has formed from a cluster of thunderstorms that emerged from Africa. The multi-day animation, above, from GOES-13, shows the steady progress of the disorganized system across the eastern Atlantic basin. Visible Imagery from GOES-13 and Meteosat-10, below, from the morning of 19 August, show the system near 40 W. The cyclonic curvature to the clouds is apparent; identification of the center in infrared imagery, below, is more difficult. Convection to the east of Danny has colder cloud top temperatures.

Meteosat-10 0.6 µm Visible Image (Top, 1200 UTC) and GOES-13 0.63 µm Visible image (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

Meteosat-10 0.6 µm Visible Image (Top, 1200 UTC) and GOES-13 0.63 µm Visible image (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

Meteosat-10 10.8 µm Infrared Image (Top, 1200 UTC) and GOES-13 10.7 µm Infrared image (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

Meteosat-10 10.8 µm Infrared Image (Top, 1200 UTC) and GOES-13 10.7 µm Infrared image (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

ASCAT Winds with GOES-13 Water Vapor Imagery (6.5 µm), 0100 UTC 19 August 2015 [click to enlarge]

ASCAT Winds with GOES-13 Water Vapor Imagery (6.5 µm), 0100 UTC 19 August 2015 [click to enlarge]

ASCAT winds from 0100 UTC on 19 August 2015 (above) show a compact circulation center with winds of 40 knots just north of 10 N and east of 40 W.

Saharan Air Layer Tracking Product [click to play animated GIF]

Saharan Air Layer Tracking Product [click to play animated GIF]

A persistent impediment to Tropical Cyclone initiation in the eastern Atlantic this year has been widespread Saharan Air Layer dust. The one-day animation, above (taken from this website), shows the SAL persists over the Atlantic; Danny has formed just to the south. Wind shear over Danny at present is weak (see below [source]), and slow strenghtening is expected as Danny approaches the Caribbean.

Mid-level Wind Shear [click to enlarge]

Mid-level Wind Shear [click to enlarge]

The Discussion from the National Hurricane Center at 0900 UTC on 19 August included this phrase: “The center is difficult to locate on infrared images,…” The Day Night Band from VIIRS on Suomi NPP can sometimes be used to locate low-level circulation centers of tropical systems. This relies on the presence of moonlight, however, and when Suomi NPP overflew Danny just before 0500 UTC on 19 August, the moon was below the horizon. Thus, the Day Night Band, below (Courtesy of William Straka) gave very little information.

VIIRS 10.35 µm Infrared Imagery and 0.70 µm Visible Imagery, 0441 UTC 19 August 2015 [click to enlarge]

VIIRS 10.35 µm Infrared Imagery and 0.70 µm Visible Imagery, 0441 UTC 19 August 2015 [click to enlarge]

More information on Danny is available at the CIMSS Tropical Weather Website. Consult the National Hurricane Center for the latest updates and official forecasts.

Super Typhoon Atsani in the West Pacific Ocean

August 19th, 2015 |

Himawari-8 infrared (10.4 µm) imagery [click to play MP4 animation]

Himawari-8 infrared (10.4 µm) imagery [click to play MP4 animation]

Super Typhoon Atsani reached Category 5 intensity early in the day on 19 August 2015; the storm displayed a nearly annular eyewall signature during much of the day on Himawari-8 infrared (10.4 µm) images (above; click image to play MP4 movie file). A large (64 Mbyte) animated GIF is available here. Evidence of low-altitude mesovortices within the eye can be seen in the 2-km resolution infrared images.

A comparison of DMSP SSMIS microwave (85 GHz) and MSAT-2 infrared (10.8 µm) images around 20 UTC is shown below (courtesy of the CIMSS Tropical Cyclones site).

DMSP SSMIS microwave (85 GHz) image and MTSAT-2 infrared (10.8 µm) image [click to enlarge]

DMSP SSMIS microwave (85 GHz) image and MTSAT-2 infrared (10.8 µm) image [click to enlarge]

On the topic of eye mesovortices, a more detailed view of these features could be seen on daylight 0.64 µm visible images (below; click image to play MP4 animation). A large (28 Mbyte) animated GIF is available here.

Himawari-8 visible (0.64 um) images [click to play MP4 animation]

Himawari-8 visible (0.64 um) images [click to play MP4 animation]

Tornado in Lake Geneva, Wisconsin

August 19th, 2015 |
GOES-14 (left) and GOES-13 (right) 10.7 µm IR images.  Lake Geneva Wisconsin is indicated by the small white box [click to play animated GIF]

GOES-14 (left) and GOES-13 (right) 10.7 µm IR images. Lake Geneva Wisconsin is indicated by the small white box [click to play animated GIF]

An EF-1 Tornado struck Lake Geneva, WI after sunset on 18 August 2015 (SPC Storm Reports; NWS MKX report). GOES-14 was in SRSO-R mode, providing 1-minute imagery over the region; additionally, GOES-13 was in RSO mode, providing imagery about every 7 minutes. Unfortunately, GOES-14 requires two 15-minute breaks in scanning to perform housekeeping (Link); one of those periods is from 0130-0145 UTC, 13 minutes before the tornado touchdown at 0158 UTC. (GOES-R will not require these 15-minute breaks). The animation above pauses during that housekeeping time; it also slows for the ten minutes surrounding 0158 UTC. (Click here for an animation without the White Box signifying Lake Geneva).

The 0158 UTC imagery from GOES-14 (paired with the 0155 UTC imagery from GOES-13 is shown below. An overshooting top that is associated with the tornado is apparent (northeast of Lake Geneva because of the parallax shift). This overshoot is easily traceable in the 1-minute imagery, above, as it moves northeastward towards Lake Michigan. The feature also appears and can be tracked in GOES-13.

GOES-14 (left) and GOES-13 (right) 10.7 µm IR images, 0158 UTC 19 August 2015.  Lake Geneva Wisconsin is indicated by the small white box [click to enlarge]

GOES-14 (left) and GOES-13 (right) 10.7 µm IR images. Lake Geneva Wisconsin is indicated by the small white box [click to enlarge]

Automated detection of Overshooting Tops (and thermal couplets) (from this website) showed a cluster of Overshooting Tops moving over southeast Wisconsin at the time of the tornado. The number of Overshoots detected jumped about an hour before the tornado touchdown.

GOES-13 Automated Detection of Overshooting Tops (blue) and Thermal Couplets (Red) 2330 UTC 18 August 2015 - 0225 19 August 2015 [click to enlarge]

GOES-13 Automated Detection of Overshooting Tops (blue) and Thermal Couplets (Red) 2330 UTC 18 August 2015 – 0225 19 August 2015 [click to enlarge]

Twin Typhoons in the western Pacific

August 17th, 2015 |

Himawari-8 10.35 µm IR images [click to play animated GIF]

Himawari-8 10.35 µm IR images [click to play animated GIF]

Himawari-8 captured the trek of Typhoons Goni (on the left) and Atsani (on the right) as they moved across the central Pacific Ocean on Monday 17 August 2015 (animation also available here as an mp4). Goni has passed through the northern Mariana Islands and is forecast to fluctuate in intensity as it moves towards Asia. Atsani’s predicted path is towards the northwest; it is forecast to intensify to a Category 5 Super Typhoon. Both storms are moving across very warm ocean waters (Goni, Atsani), and deep layer wind shear values are low (below). Sea Surface Ttemperature and Wind Shear products are available from the CIMSS Triopical Cyclones site.

Satellite-derived Wind Shear over the Pacific Ocean, 1800 UTC 17 August 2015 [click to enlarge]

Satellite-derived Wind Shear over the Pacific Ocean, 1800 UTC 17 August 2015 [click to enlarge]

Late in the day on 17 August, a comparison of MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) imagery of Category 3 Typhoon Atsani around 2232 UTC (below) showed a rather ragged-looking eye on the infrared image and evidence of a eyewall replacement cycle (ERC) occurring on the microwave image. The ERC process often indicates that a change in tropical cyclone intensity will soon take place.

MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) images of Typhoon Atsani [click to enlarge]

MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) images of Typhoon Atsani [click to enlarge]

What is remarkable in this case of “twin typhoons” in the West Pacific basin is that the MIMIC-TC product indicated that both Atsani and Goni were undergoing ERCs at about the same time (below).

MIMIC-TC product for Typhoon Atsani [click to enlarge]

MIMIC-TC product for Typhoon Atsani [click to enlarge]

MIMIC-TC product for Typhoon Goni [click to enlarge]

MIMIC-TC product for Typhoon Goni [click to enlarge]

A multi-day YouTube animation of Himawari-8 10.35 µm infrared imagery shows the upscale development of Goni and Atsani in the central Pacific. The loop runs from 13 August through 1200 UTC on 18 August.