Detection of convective initiation and the first tornado in March

March 9th, 2010 |

After an unusually quiet February tornado-wise in the United States (only one tornado was reported, an EF-0 in California that lasted for 3 minutes late in the day on February 27th), two tornadoes touched down near sunset in western Oklahoma, near the town of Hammon. The above animation from NAWIPS shows 1-km GOES-12 visible imagery with superimposed contours of cloud-top cooling (and lightning strikes) from about 2000 UTC on 9 March to 0015 UTC on the 10th, shortly after tornado touchdown (the tornado location is indicated by the red triangle in the animation). The growing cell that will ultimately spawn the tornado is correctly identified. Such cloud-top cooling is computed routinely as part of a University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (CIMSS) project on convective initiation. The algorithm locks on to the convective cell that spawns the tornado, and not adjacent cells. The strongest cooling was associated with the storm that produced the tornado.

If the detected cloud-top cooling is co-located with changes in cloud phase (for example, from supercooled water droplets to ice crystals, or from all water droplets to supercooled water droplets) as inferred from GOES-12 radiances for different infrared channels, then convective initiation is deemed to be ongoing. In this animation of 11-micron cloud temperatures overlain with Convective Initiation, note the CI Likely at 2132 UTC along the Texas/Oklahoma border. Note that only the nascent cell that subsequently produces a tornado is identified, as only that cell contains the required strong cooling and the phase changes. That region of cloud top cooling and phase change then moves north-northeastward as the convective cell that spawned the tornado develops. Convective Initiation is no longer indicated, however, because the initiation stage of convection is over by 2200 UTC.

(Added: CNN has Andy Gabrielson’s too-close-for-comfort video).

(Added: Another video, from YouTube).

(One more Addition: Write up on the tornadic event from the Norman, OK office of the National Weather Service).

Another tropical cyclone in the South Atlantic Ocean!

March 9th, 2010 |
Meteosat-9 10.8 µm IR images

Meteosat-9 10.8 µm IR images

EUMETSAT Metetosat-9 10.8 µm IR images (above; also available as a QuickTime movie) showed the evolution of a disturbance that had all the appearances of being another example of a rather rare event: a subtropical cyclone in the South Atlantic Ocean (off the southeast coast of Brazil) during the 09 March 2010 – 10 March 2010 time period.

This system was eventually declared to be tropical cyclone on 10 March, according to this HPC discussion:

SOUTH AMERICA SYNOPTIC DISCUSSION
INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER
CAMP SPRINGS MD
847 AM EST WED MAR 10 2010

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

SYNOPSIS (VALID FROM 00Z MAR 10). THE UPPER LEVEL ANALYSIS SHOWS A CLOSED LOW NEAR 33S 45W EXTENDING A SHORT WAVE TROUGH TO THE NORTHWEST INTO BRASIL ALONG 20S 50W. THIS FEATURE IS DECOUPLING FROM A WARM CORE SURFACE LOW OFF THE COAST OF BRASIL…WITH CLOSED CIRCULATION ESTIMATED NEAR 29.6S 48.2W. ALTHOUGH A TIGHT/COMPACT STORM…IT IS NOW CLASSIFIED AS A TROPICAL CYCLONE RATHER THAN SUBTROPICAL.

On 13 March this storm was given the name “Anita” by the Brazilian MetSul weather center . Note that Brazil has only had one documented case of a land-falling tropical cyclone that had reached hurricane intensity — “Catarina” in March 2004.

A false-color NOAA-19 Red/Green/Blue (RGB) image using channels 01/02/04 (below) displayed a nice view of the tropical cyclone on 10 March. The low-level circulation (clouds with a slightly yellow hue) was becoming partially exposed, with a large burst of convection occurring in the southwest quadrant of the cyclone.

NOAA-19 false-color Red/Green/Blue (RGB) image

NOAA-19 false-color Red/Green/Blue (RGB) image

On a closer view using the corresponding NOAA-19 10.8 µm IR image (below), note the presence of a packet of gravity waves which was propagating southwestward away from the region of coldest overshooting tops (which were around -70º C, darker black color enhancement).

NOAA-19 10.8 µm IR image

NOAA-19 10.8 µm IR image

A later animation of IR imagery from the CIMSS Tropical Cyclones site (below) showed the development of additional convective bursts within the southern portion of the cyclone. Even well to the northwest of the center of the circulation, there was a ship report showing wind speeds of 35 knots.

IR images + ship reports

IR images + ship reports

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IR image + deep layer wind shear

IR image + deep layer wind shear

The tropical cyclone formed in an environment characterized by a moderate amount of deep layer wind shear (above), over a region of sea surface temperatures that were near 25º C (below).

Sea surface temperature analysis

Sea surface temperature analysis

Additional details and images of this South Atlantic tropical cyclone can be found at the Weather Underground, AccuWeather, and NASA.