Tropical Cyclone Report (TCR); Tropical Storm Tony

By: KoritheMan , 2:45 PM GMT on March 19, 2013

Tropical Cyclone Report
Tropical Storm Tony
22 October-25 October 2012

Tony was a short-lived tropical storm that formed over the central Atlantic about midway between the northern Leeward Islands and the Azores. Tony had no impact on land.

a. Synoptic History

Tony developed from a tropical wave that moved off the coast of Africa on 11 October. The southern portion of the wave moved westward and spawned Hurricane Sandy in the Caribbean Sea. The wave was ill-defined and not easily trackable in satellite images. At the same time, a sharp and very well-defined upper cold low and accompanying mid- to upper-level trough extending its cyclonic vorticity down to below 500 mb was in existence over the eastern Atlantic between the Cape Verde Islands and the Lesser Antilles. This feature moved westward roughly in tandem with the tropical wave for the next several days. The northern portion of the wave fractured and began to move west-northwest on 13 October. The interaction of these two features resulted in a large area of disturbed weather over the eastern Atlantic. The northern portion of the tropical wave moved very slowly over the next several days while continuing to move in tandem with the upper-level system. The latter system weakened and slowly became more elongated during this time, likely due to a loss of upper air support and warm air advection associated with the tropical wave. The tropical wave became the dominant feature, and a broad surface low formed in connection with it on 19 October. The trough continued to weaken and move westward, which resulted in a less hostile environment. At the same time, another upper-level trough was in the process of undergoing amplification over the western Atlantic, which caused the budding disturbance to turn toward the northwest toward a weakness in the ridge. Concentrated bands of convection persisted around the center, and, within an environment of relatively light vertical wind shear, the low became a tropical depression around 1800 UTC 22 October while centered midway between the northern Leeward Islands and the Azores. The “best track” chart of the tropical cyclone’s path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively (to be added). The best track positions and intensities are listed in Table 1 (to be added). The depression initially failed to strengthen, possibly due to a relatively dry environment. A burst of deep convection occurred over the low-level center around 1200 UTC the next day, and it is estimated that the cyclone reached tropical storm strength at that time.

Tony quickly turned northward and then northeastward as southwesterly mid-level flow associated with an upper trough to the west began to impinge on the system. The cyclone gradually strengthened, reaching its peak intensity of 50 kt near 0600 UTC 24 October. Available microwave data suggested a mid-level eye feature at that time. The satellite presentation and convective pattern began to degrade after 1200 UTC as Tony entered an environment of increasing southwesterly shear and cooler waters, but winds were slow to decrease even though the associated convection was relatively shallow. This could have been due to a strong pressure gradient between Tony and the Bermuda-Azores ridge, which is undulatingly stronger in this region of the Atlantic. Its circulation elongated east-northeast to south-southwest, Tony became an extratropical remnant low pressure system near 1800 UTC 25 October while located about 600 miles southwest of the Azores.

b. Meteorological Statistics

Observations in Tony (Figs 2 and 3, to be added) include the satellite-based Dvorak technique from the Tropical Analysis and Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB). Objective ADT estimates from the University of Wisconsin CIMSS was also used. Scatterometer and microwave data were useful in determining when Tony's circulation had become distorted on 25 October.

Tony's peak intensity of 50 kt is a little higher than the Dvorak consensus (although CI numbers using the CIMSS ADT were as high as 55 kt during the time of peak intensity)., and is based primarily on several microwave passes over the cyclone from about 0300 UTC to 0900 UTC showing a well-defined mid-level eye feature, which is normally characteristic of strong tropical storms. The general Dvorak consensus was at 3.0 during that time, which translates to 45 kt, so this report isn't in too large a conflict with the available satellite estimates. An image of the closest microwave pass to peak intensity is shown below in Figure 5.

c. Casualty and Damage Statistics

Since Tony was a marine interest, there were no reports of damage or fatalities.

d. Forecast and Warning Critique

The genesis of Tony was not very well predicted. The precursor disturbance was first mentioned around 0000 UTC 21 October and given a "medium" chance (30%) of development. This was about 36 hours prior to genesis. Genesis probabilities increased to 40% about 24 hours later, or about less than a day prior to formation.

Average track forecast errors with Tony were fairly small, although it was a little too short-lived to garner a meaningful forecast evaluation. Even prior to formation, the global models were in excellent agreement on the future path of Tony, which was controlled primarily by an upper-level trough over the central Atlantic.

Intensity forecast errors were fairly small as well, although the timing of Tony's peak intensity was off by about a day.

No watches or warnings were issued with Tony since it remained far away from land.

Infrared satellite image of Tony at peak intensity.

AMSUB microwave pass of Tony showing a well-defined mid-level eye feature. The pass was taken at 0446 UTC 24 October, right around the time Tony is assumed to have reached its peak intensity.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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2:47 PM GMT on March 19, 2013
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