Hurricane Fred

August 31st, 2015

GOES-13 Visible (0.63 um) and Infrared (10.7 um) images [click to enlarge]

GOES-13 Visible (0.63 um) and Infrared (10.7 um) images [click to enlarge]

Tropical Storm Fred reached hurricane intensity east of the Cape Verde Islands late in the day on 30 August 2015.  As mentioned in the NHC discussion on the following morning, Fred was the first hurricane to pass through the Cape Verde Islands since 1892. While no central eye was apparent on GOES-13 (GOES-East) Visible (0.63 um) and Infrared (10.7 um) images at 0845 UTC (above), a DMSP SSMIS 85 GHz microwave image sourced from the CIMSS Tropical Cyclones site did reveal a small eye at 0904 UTC (below).

DMSP SSMIS 85 GHz microwave image [click to enlarge]

DMSP SSMIS 85 GHz microwave image [click to enlarge]

Later in the day, a few Tropical Overshooting Tops were analyzed using Meteosat-10 Infrared (10.8 um) imagery (below).

Meteosat-10 Infrared (10.8 um) images with overlay of Tropical Overshooting Top product [click to enlarge]

Meteosat-10 Infrared (10.8 um) images with overlay of Tropical Overshooting Top product [click to enlarge]

More information about Hurricane Fred can be found here.

Tropical Storm Erika approaches the eastern Caribbean

August 26th, 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]

GOES-13 Infrared Imagery (above) for the 24 hours ending 1415 UTC on 26 August 2015 show Tropical Storm Erika approaching the Leeward Islands of the eastern Caribbean. A general increase in convection in the 24 hours shown is obvious. Visible imagery (below) from the morning of 26 August shows some overshooting tops within the central dense overcast (CDO) covering the low-level circulation. A plot of the number of overshooting tops in Erika is here (taken from this webpage). Outward-propagating gravity waves can also be seen at the top of the CDO.

GOES-13 Visible Imagery (0.63 µm) [click to play animated GIF]

GOES-13 Visible Imagery (0.63 µm) [click to play animated GIF]

Surface winds as observed by the Metop ASCAT Scatterometer early on 26 August (0056 UTC), below, show a modest circulation with winds that are mostly below tropical storm force (Added: The 1411 UTC image, bottom, shows some tropical-storm force wind flags). Dry Saharan Air Layer air should not limit intensification of Erika, but wind shear just north and west of the storm is strong (SAL and Wind Shear imagery taken from the CIMSS Tropical Cyclones site).

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm) [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm), ~0100 UTC 26 August 2015 [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm) [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm), ~1400 UTC 26 August 2015 [click to enlarge]

For the most recent forecasts on Erika’s future, see the National Hurricane Center website.

Hurricane Danny

August 21st, 2015

GOES-14 visible (0.63 um) images [click to play MP4 animation]

GOES-14 visible (0.63 um) images [click to play MP4 animation]

1-minute interval GOES-14 SRSO-R visible images (above; click to play MP4 animation; also available as a 130 Mbyte animated GIF) showed the eye and surrounding cloud structure of Category 2 Hurricane Danny on 21 August 2015. The hazy signature of a dust-laden Saharan Air Layer (SAL) could be seen to the west, northwest, and north of the storm.

Meteosat-10 Saharan Air Layer (SAL) product [click to play animation]

Meteosat-10 Saharan Air Layer (SAL) product [click to play animation]

The compact circulation of Danny remained fairly “isolated” from the multiple pockets of SAL which stretched westward across much of the tropical Atlantic Ocean (above). The relatively clear dust-free air surrounding Danny was tropical moisture being wrapped northward into the circulation from the Intertropical Convergence Zone (ITCZ), as seen with the MIMIC Total Precipitable Water product (below).

MIMIC Total Precipitable Water product [click to enlarge]

MIMIC Total Precipitable Water product [click to enlarge]

A close-up view of Hurricane Danny (below; click image to play MP4 animation) showed some interesting detail in the convective bursts within the eyewall region, in spite of the very oblique satellite viewing angle. There is also a large (165 Mbyte) animated GIF available here.

GOES-14 visible (0.63 µm) images [click to play MP4 animation]

GOES-14 visible (0.63 µm) images [click to play MP4 animation]

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 Imagery (Top, 1200 UTC) and GOES-13 0.63 µm Visible imagery (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

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

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

Meteosat-10 10.8 µm Visible Imagery (Top, 1200 UTC) and GOES-13 10.7 µm Visible imagery (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.