Tropical Depression Nine (now: Tropical Storm Ida) in the western Caribbean

August 26th, 2021 |
VIIRS I01 (0.64 µm) imagery with ACSPO SSTs plotted in clear regions, 1838 UTC on 26 August 2021 (Click to enlarge)

The National Hurricane Center is issuing advisories on a strong Tropical Depression in the western Caribbean Sea, centered to the west of Jamaica — in the southeast corner of the image above. This system is at the edge of the observing capabilities from the CIMSS Direct Broadcast antenna, but the image above, created from that data stream, does show the very warm Gulf of Mexico waters over which the system is forecast to move (much of the orange/red enhancement shows temperatures at/above 30 C/86 F!)

AMSR-2 Microwave imagery from JAXA‘s GCOM-W1 satellite, below, shows an unorganized storm, but plenty of ongoing convection. At the time of this imagery (1802 UTC), the storm was centered near 17.5 N, 69.5 W.

AMSR-2 imagery at 36.5 and 89.0 GHz, 1814 UTC on 26 August 2021 (Click to enlarge)

More information on this system is available at the National Hurricane Center. When named, this storm will be Ida.


Ida was named shortly after 2100 UTC on 26 August. Day Night Band imagery at 0658 UTC on 27 August 2021, below, shows Ida south of Cuba, with indication of shear: the strong convection is displaced slightly to the northeast of the surface circulation (inferred by the curvature in the low-level cumulus). Ida at this time displayed no lightning activity (unlike the convection in the central Gulf of Mexico).

VIIRS Day-Night Band visible (0.70 µm) imagery, 0658 UTC 27 August 2021 (click to enlarge)

Tropical Storm Henri just north of the Bahamas

August 20th, 2021 |
GOES-16 Band 2 Visible (0.64) imagery, 1306 – 1525 UTC (Click to enlarge)

GOES-16 Visible Imagery, above, shows Tropical Storm Henri east of Florida and to the north of the Bahamas. Cirrus outflow is well-developed to the east and south, but the storm is sheared; the surface circulation is near the northwestern edge of the ongoing deep convection. Persistent northerly shear, as shown below in a figure taken from the CIMSS Tropical Website, shows Henri moving from a region of relatively high shear towards a region of relatively smaller shear.

200-850 mb shear analysis at 1400 UTC on 20 August 2021. The latest NHC forecast is also shown, with a landfall as of early Friday 20 August forecast over southern New England late Sunday 22 August 2021.

GCOM-W1 overflew Henri at 0616 UTC on 20 August. Microwave imagery, below, (retrieved from the AOML Direct Broadcast site) confirm the sheared nature of the storm at that time. Both frequencies show that deep convection is displaced to the south of the storm center.

GCOM-W1 AMSR-2 Microwave imagery at 36.5 and 89.0 GHzm 0616 UTC on 20 August 2021 (Click to enlarge)

Suomi NPP overflew the storm at around 0600 UTC, and the toggle below shows the Day Night band visible (0.7 µm) imagery and the I05 infrared (11.5 µm) imagery; included in the toggle are Advanced Clear Sky Processor for Oceans (ACSPO) SST values in clear regions. Atlantic Ocean waters have surface temperatures in the 84-85º F range. Cloud top temperatures are as cold as -86º F for this overpass. (Suomi NPP VIIRS data were processed at the CIMSS Direct Broadcast site and injected into AWIPS).

Suomi NPP VIIRS Day Night Band Visible (0.7 µm) and I05 Infrared (11.5 µm) imagery, along with an ACSPO SST analysis in clear regions, 0556 UTC on 20 August 2021 (Click to enlarge)

The animation of the Airmass RGB, below, shows a prominent feature over the mid-Atlantic states of the United States that will have a big role in Henri’s future path: a mid-tropospheric potential vorticity maximum highlighted as red/orange in the Airmass RGB. The toggle at bottom compares the 1211 UTC Airmass RGB with contours of pressure (mb) on the 1.5 PVU surface.

GOES-16 Airmass RGB, 0611-1556 UTC on 20 August 2021 (Click to enlarge)

For the latest on Henri, refer to the National Hurricane Center Website. Residents of southern New England and Long Island and New Jersey in particular should pay close attention to this storm.

Hurricane Grace in the Caribbean

August 18th, 2021 |
Suomi-NPP Infrared (I05, 11.5 µm), Day Night Band Visible (0.7 µm) and Infrared with ACSPO SST values, 0626 UTC on 18 August 2021 (Click to enlarge). Data from the CIMSS Direct Broadcast site

Grace (then a tropical storm) is shown in AWIPS above, in between Jamaica and the Caymans, in Day Night Band Visible imagery, along with VIIRS I05 Infrared imagery, from 0626 UTC, using data from the Direct Broadcast site at CIMSS. The coldest cloud tops with the most vigorous convection, shown as white/blue in the color enhancement, are near -89º C. The visible imagery has sufficient lunar illumination (more than on Monday 16 August with Fred!) that the tallest cloud tops are casting shadows. The few cloud-free pixels that are present allow ACSPO sea-surface temperatures to be computed: 30º C or 86º F.

NOAA-20 and Suomi-NPP give infrequent views of the storm. GOES-16 is the better choice for storm monitoring. The animation below shows the Convection RGB over the storm. The Convection RGB is useful because it can highlight regions of vigorous convection (in orange/yellow). The RGB highlights convective banding near the center of the storm and also on the periphery of the storm.

GOES-16 Day Convection RGB over Grace, 1346 – 1611 UTC on 18 August 2021 (Click to enlarge)

GOES-16 Water Vapor imagery, below, shows the environment in which the storm is forming. The upper-level water vapor imagery, 6.19 , below, begins near the time of the Suomi-NPP overpass (imagery shown above)and continues until about 1600 UTC. It shows a rapid organization to the storm — certainly the satellite presentation changes over the 10 hours of this animation! There does seem to be dry air to the north of Grace, just north of Cuba. How that affects the storm in the future is to be determined.

GOES-16 Upper Level Water Vapor Infrared imagery (Band 8, 6.19 µm) , 0636 UTC to 1621 UTC (Click to enlarge)

Total Precipitable Water fields, below, for the 24 hours endings at 1500 UTC on 18 August, also show some dry air near the storm. However, Grace has access to plenty of moisture in the near term. Tropical storm Henri, Pacific Hurricane Linda, and the remains of Fred are also apparent in the imagery.

MIMIC Total Precipitable Water, 1600 UTC 17 August – 1500 UTC 18 August (Click to enlarge)

Grace is in an environment of low shear, and is over very warm water, as shown in this image, a 1500 UTC 200-850 mb shear and SST analysis taken from the CIMSS Tropical Website.


GCOM-W1 AMSR-2 Imagery at 36.5 and 89.0 GHz, 1903 UTC on 18 August 2021 (Click to enlarge)

JAXA‘s GCOM-W1 satellite, carrying the AMSR-2 instrument, overflew Grace near 1900 UTC on 18 August, and imagery (taken from the AOML Direct Broadcast website) from 36.5 and 89.0 GHz is shown above (note that 89.0 GHz imagery is used in MIMIC-TC imagery available at the CIMSS Tropical Website). Both microwave representations show a distinct eye in the storm, most especially at lower levels.

True-Color imagery from CSPP Geosphere, below, shows convection persistently developing around the storm center as it moves through the northwest Caribbean towards the Yucatán Peninsula.

True Color imagery from CSPP Geosphere, 1400 – 1950 UTC on 18 August 2021 (click to animate)

More information on Grace is available at the National Hurricane Center.

Using Polar-Orbiting Satellite Imagery from Direct Broadcast sites to understand Elsa

July 6th, 2021 |

Suomi NPP Adapative Day Night Band imagery, 0636 UTC on 6 July 2021 (Click to enlarge)

AOML (The Atlantic Oceanographic and Meteorological Laboratory) maintains a Direct Broadcast antenna site that holds satellite imagery (created using CSPP — the Community Satellite Processing Package) created when a tropical system — such as Elsa — is within the download footprint of the AOML antenna.  This imagery — particularly in the microwave — is useful to describe the system’s structure. The Day Night Band image above, from Suomi NPP at 0636 UTC, shows a non-symmetric storm with the bulk of clouds to the east and south of the surface center (at that time near 23.9 N, 82.3 W, i.e., in the Florida Straits to the south of Dry Tortuga).  Rainfall, as diagnosed using MIRS algorithms and microwave ATMS (Advanced Technology Microwave Sounder) data from NPP, below, shows the asymmetry of the storm as well:  almost all the diagnosed rain is east of the center. (It’s helpful that both infrared imagers and microwave sounders are on the same satellite!)

Suomi NPP ATMS-derived Rain Rate, 0637 UTC on 6 July 2021 (Click to enlarge)

The GCOM-W1 (supported by JAXA) satellite also scanned Elsa shortly before 0700 UTC on 6 July.  Microwave observations at ~36 GHz, below, and at 89 GHz, farther below, can help to characterize the structure of the storm. Indeed, observations at/around 85-89 GHz are used in the MIMIC TC product as described here.

GCOM AMSR-2 observations at 36.5 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

GCOM AMSR-2 observations at 89.0 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

In addition to the AOML site, the CIMSS Direct Broadcast site contains Polar Orbiting imagery in near-real time. The afternoon 88.2 GHz image from (NOAA-20) ATMS is shown below.  Cold cloud tops associated with strong scattering by ice of the 88.2 GHz signal are apparent.

NOAA-20 ATMS Channel 16 Brightness Temperature, 1845 UTC on 6 July 2021 (Click to enlarge)


There are a multitude of polar orbiters such that observations show up in clusters of time.  However, for a better time animation, it’s still best to rely on GOES-16!  The animation below, from CSPP Geosphere, shows a sheared storm south and west of Ft Myers FL.  Indeed, an 1800 UTC 6 July 2021 shear analysis from the CIMSS Tropical website (here, from this site), shows westerly shear of 25-30 knots.

GOES-16 True-Color imagery, 6 July 2021 from 1730 to 1920 UTC (Click to animate)

For the latest information on Elsa, consult the webpages of the National Hurricane Center, or the SSEC/CIMSS Tropical Weather Page.