Tropical Storm (formerly Hurricane) Humberto

September 16th, 2013 |
GOES-13 10.7 µm IR channel image (with track of Humberto)

GOES-13 10.7 µm IR channel image (with track of Humberto)

A GOES-13 10.7 µm IR channel image with the track of Humberto from the CIMSS Tropical Cyclones site  (above) showed that the storm (which became the first hurricane of the season in the Atlantic Basin on 11 September) had been meandering over the eastern North Atlantic Ocean for several days, eventually weakening to a post-tropical cyclone on 14 September before re-organizing into a tropical storm early in the day on 16 September (NHC advisories archive).

GOES-13 0.63 µm visible channel image (with ASCAT surface scatterometer winds)

GOES-13 0.63 µm visible channel image (with ASCAT surface scatterometer winds)

A GOES-13 0.63 µm visible channel image with an overlay of ASCAT surface scatterometer winds (above) showed evidence of tropical storm force winds (yellow wind barbs) north of the storm center at 13:17 UTC. Note the presence of a well-defined cloud vortex located southwest of the 18 UTC center fix position.The NHC discussion #26 mentioned that several smaller-scale vortices had been rotating around the mean circulation center of Humberto — and a close-up view using GOES-13 0.63 µm visible channel images (below; click image to play animation) revealed one of these exposed vortices to the southwest of the center of Humberto.

GOES-13 0.63 µm visible channel images (click images to play animation)

GOES-13 0.63 µm visible channel images (click images to play animation)

See From the Lee Side for a discussion on the role of vertical wind shear on tropical cyclones such as this.

GOES-13 Sounder Anomalies

September 16th, 2013 |
GOES-13 10.7 µm IR channel images (click unage to play animation)

GOES Sounder DPI Lifted Index from 1300 UTC 15 September

The GOES-13 Sounder has been experiencing an increased number of unexpected scan line lengths. This was originally detected on 1 July 2013 and it has become more common since 12 September 2013. The anomaly is manifest in the data by occasional pixel gaps in all channels of the Sounder images. Some images show only a single gap (and therefore just one missing pixel); other images have several gaps. In the image above, the missing values are the black pixels just off the North Carolina coast (for example), or near the Mississippi River in southwestern Mississippi. Note that missing data only is present in the GOES-13 part of the domain. The GOES-15 signal is clean. The root cause of this error is under investigation. From NESDIS: “No telemetry violations have occurred, and all Sounder filter wheel telemetry data, including Filter wheel currents and period monitors, are within expected values.”

The missing pixels are also present in the real-time Sounder data available at CIMSS at this link. An example from September 15th is shown below. Or, click here for a composite (GOES-13/GOES-15) single-band image.

GOES-13 10.7 µm IR channel images (click unage to play animation)

GOES Sounder DPI Lifted Index from 1300 UTC 15 September

A quick analysis at two times (0246 and 1446 UTC) suggests that prior to 28 August, errors per image were limited to 20 or so pixels. Between 28 August and 9 September, fewer than 100 pixels were affected each hour. Since 10 September, the number of pixels affected in each image has increased one some days to more than 200. There are nearly 64000 pixels in each sounder image, so the number of bad points remains a small percentage of the total.