Tropical Depression #1

May 28th, 2009 |
GOES-12 10.7 µm IR images

GOES-12 10.7 µm IR images

The first tropical depression of the 2009 season formed off the US East Coast on 28 May 2009. An AWIPS animation of GOES-12 10.7 µm “IR window” images (above) revealed several bursts of convection as the canopy of cold cloud tops slowly increased in areal coverage.

One of the convective bursts occurred around 15:00 UTC , and a comparison of the 1-km resolution MODIS 11.0 µm IR window and the 4-km resolution GOES-12 10.7 µm IR window images around that time (below) depicted cloud top brightness temperatures several degrees colder on the MODIS image (-72º C, vs -68º C on the GOES-12 IR image).

MODIS 11.0 µm and GOES-12 10.7 µm IR images

MODIS 11.0 µm and GOES-12 10.7 µm IR images

Products from the CIMSS Tropical Cyclones site (below) showed that the coldest SSM/I microwave brightness temperatures (red colors) were found in the southeastern quadrant of the cold IR cloud shield. In addition, it could be seen that the tropical depression was situated over the warmer waters of the Gulf Stream (SST values greater than 24º C, green colors), which was likely aiding in the intensification process. The deep layer wind shear was also light, which was another factor that favored further intensification.

GOES-12 IR + DMSP Microwave + Sea Surface Temperature

GOES-12 IR + DMSP Microwave + Sea Surface Temperature

The Blended Total Precipitable Water product (below) showed that TPW values were as high as 50-57 mm (2.0 to 2.2 inches, red colors) in the vicinity of the tropical depression. The POES AMSU Rainfall Rate product depicted rainfall intensities as great as 29 mm per hour (1.14 inch per hour) around 13:30 UTC.

Blended Total Precipitable Water + GOES-12 IR images

Blended Total Precipitable Water + GOES-12 IR images

===== 29 MAY UPDATE =====

On the following day (29 May 2009), GOES-12 visible images from the CIMSS Tropical Cyclones site (below) indicated that the low-level circulation  had become separated from the cluster of deep convection which was located in the southeast  quadrant of the tropical depression — this was due to increasing amounts of deep layer wind shear across the region.

GOES-12 visible images

GOES-12 visible images

Convection in the Gulf of Mexico

May 28th, 2009 |
MODIS 11.0 µm IR + GOES-12 10.7 µm IR images

MODIS 11.0 µm IR + GOES-12 10.7 µm IR images

AWIPS images of the 1-km resolution MODIS 11.0 µm  and the 4-km resolution GOES-12 10.7 µm “IR window” channels (above) showed a cluster of very cold cloud top temperatures (-88º C on MODIS, and -82º C on GOES, violet colors) associated with deep convection over the northwestern Gulf of Mexico on 28 May 2009. Also of interest is the appearance of  both transverse banding and an orthogonal gravity wave structure in the northwestern portion of the anvil edge (near the Mexico border).

A comparison of the MODIS 0.6 µm “visible channel”, 1.3 µm “cirrus detection channel”, 6.7 µm “water vapor channel”, and the 11.0 µm “IR window channel” (below) showed that the various satellite  channels differed in their  ability to detect the true western and northwestern extent of the cirrus anvil edge.

MODIS IR, visible, cirrus, and water vapor channel images

MODIS visible, cirrus detection, water vapor, and IR window channel images