Hurricane Cristobal and the Saharan Air Layer

August 28th, 2014
Meteosat-10 Saharan Air Layer product (click to play animation)

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

The CIMSS Saharan Air Layer (SAL) product (above; click image to play animation) showed a large pocket of SAL (yellow to red color enhancement) drifting westward over the far western Atlantic Ocean and toward the Gulf of Mexico on 28 August 2014.

On GOES-13 0.63 µm visible channel images (below; click image to play animation), the hazy signature of the SAL dust could be seen surging westward, not far to the south of Category 1 intensity Hurricane Cristobal.

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

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

The SAL also exhibited a warm/dry signature (yellow to orange color enhancement) on the corresponding GOES-13 6.5 µm water vapor channel images (below; click image to play animation).

GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)

At 17:16 UTC, a Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth web map server (below) showed that Hurricane Cristobal had developed an eye formation.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

A comparison of AWIPS-2 images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data (below) revealed that the coldest cloud-top IR brightness temperatures (-77º C, lighter gray color enhancement) were located within convection just southwest and southeast of the eye.

Suomi NPP VIIRS 0.64 µm visible image and 11.45 µm IR channel image

Suomi NPP VIIRS 0.64 µm visible image and 11.45 µm IR channel image

Stray Light in GOES-13 Imagery

August 27th, 2014
GOES-13 3.9 µm infrared channel images (click to play animation)

GOES-13 3.9 µm infrared channel images (click to play animation)

GOES-13 is currently in Autumn Eclipse Season, when the Earth-Satellite-Sun geometry means that solar energy can reach the satellite sensors directly. NOAA NESDIS has software to mitigate the effects of Stray Light in the Sensor Processing System (SPS) that transforms the raw GOES Imager data to navigated and calibrated (GVAR) data. However, earlier this month, the SPS at Wallops inadvertently omitted the Stray Light Correction. The animation above, from 16-27 August, shows how Stray Light intruded into the 3.9 µm imagery on the GOES-13 Imager; on 25 August the Stray Light Correction was turned back on, and the final two images show no major Stray Light effects over the satellite view (Stray Light is still recorded in outer space). The animation above is for 5:15 UTC, when Stray Light affected the eastern part of the full disk scan. At 4:45 UTC, Stray Light affected the western part of the disk, and at 05:00 UTC, the central part of the disk.

Click here for more about the Stray Light Correction.

GOES-14 SRSOR: Mesoscale Convective Vortex in the Southern Mississippi Valley

August 18th, 2014
GOES-14 0.63 µm visible channel images (click to play animation)

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

The GOES-14 satellite was in Super Rapid Scan Operations for GOES-R (SRSOR) mode providing 1-minute imagery over the eastern US on 18 August 2014. From the late morning into the afternoon hours, 0.63 µm visible channel images (above; click image to play animation; also available as an MP4 movie file or a YouTube video) revealed a large and well-defined mesoscale convective vortex (MCV) propagating eastward across northern Mississippi. This MCV was spawned from a thunderstorm which rapidly developed over far southwestern Arkansas during the preceding nighttime hours (beginning around 06:15 UTC: GOES-13 IR images).

A comparison of Suomi NPP VIIRS 11.45 µm IR channel images (below) showed the rapid growth of the parent thunderstorm from 07:18 UTC to 08:59 UTC. The coldest cloud-top IR brightness temperatures were -80º C.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

Historic Rainfall in Islip, NY

August 13th, 2014
GOES-13 10.7 µm infrared imagery on 13 August 2014; The Islip airport (KISP) is at the violet square (click to animate)

GOES-13 10.7 µm infrared imagery on 13 August 2014; The Islip airport (KISP) is at the violet square (click to animate)

The system that caused flooding in Detroit, MI on 11 August and in Baltimore/Washington on 12 August has moved eastward: Islip, NY, on central Long Island, had historically heavy rainfall early in the morning on 13 August as more than 13″ of rain fell (9.71″ in two hours, and 5.34″ in one hour!!), smashing the New York state record for 24-hour rainfall (Record Event Report).

The GOES-13 animation above shows the satellite presentation of the storms that produced the heavy rainfall (the heaviest rain fell between 0900 and 1100 UTC). It is immediately apparent that the deepest convective clouds were not responsible for the heavy rains: cloud-top IR brightness temperatures over Islip were only near -30º C (per the 1200 UTC OKX sounding, that was around 300 hPa; the tropopause was closer to 150 hPa) and cloud-to-ground lightning was not detected. Winds at the Islip airport shifted from easterly/northeasterly to southeasterly as the heavy rains ended (time series plot of surface weather): an approaching frontal boundary may have helped force the heavy rains.

The animation shows continual cold cloud redevelopment at/near Islip, suggesting that training shower development was an important factor in the flooding.

Although the region was generally cloudy, holes in the cloud cover revealed GOES-13 sounder Total Precipitable Water values (below; click image to play animation) of 45-50 mm or 1.8-2.0 inches over Long Island just ahead of the advancing frontal boundary. The Blended Total Precipitable Water product showed a sudden jump to over 50 mm or 2.0 inches around 10 UTC over Long Island, and these TPW values were around 150% of normal for that location and time of the year.

GOES-13 sounder Total Precipitable Water derived product images (click to play animation)

GOES-13 sounder Total Precipitable Water derived product images (click to play animation)

The MIMIC Total Precipitable Water product (below) showed a northward surge of tropical moisture into the region on 13 August.

MIMIC Total Precipitable Water (11-13 August)

MIMIC Total Precipitable Water (11-13 August)