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By: KoritheMan , 5:28 AM GMT on March 15, 2013
Tropical Cyclone Report
Tropical Storm Patty
11 October-13 October 2012
Patty was a short-lived tropical storm that formed near the central Bahamas. Patty had little impact on the islands.
a. Synoptic History
A surface trough was first noted on satellite pictures about 150 miles south of Bermuda early on 5 October. The exact origin of this trough is a bit unclear, but could have possibly been related to the large upper low which supported the frontal zone that absorbed Tropical Storm Oscar. Upper air data indicate that a rather strong mid-level ridge had built across the Bahamas, Florida, and the eastern Gulf of Mexico in the wake of the aforementioned trough. The small surface trough moved quickly southwestward steered primarily by this ridge. The disturbance became quasi-stationary near Crooked Island in the central Bahamas. At that time, there was an upper tropospheric cold low to the north of the Leeward Islands, which in combination with the western Atlantic high pressure area was apparently enough to inhibit much movement of the disturbance. A large mid-latitude trough amplified over the eastern United States, but was of relatively low amplitude and southward extent; consequently, the surface trough moved only slowly northward at speeds of about 5 kt. The trough quickly lifted out, leaving behind additional low- to mid-level ridging. As a result, the disturbance abruptly ceased its slow northward motion while convection became more persistent near the axis of the low pressure area. The low turned back to the southwest again under the influence of the ridge early on 10 October. A small upper low had developed over the eastern Gulf of Mexico and moved across the central Florida peninsula during the early morning hours of the 11th. This low contributed to persistent southwesterly shear over the disturbance and caused the low-level center to remain along the west side of the associated shower activity. Notwithstanding, the low maintained enough organized convection within 50 miles of the center to be designated a tropical depression near 0600 UTC that day while centered about 130 miles east-northeast of Eleuthera Island in the central Bahamas. 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 (to be added in the final rendition), respectively. The best track positions and intensities are listed in Table 1 (to be added in the final rendition). The depression became a tropical storm about six hours later.
Patty moved less than 75 miles from its systematic point of origin as it remained within an environment of weak steering lacking any appreciable synoptic forcing mechanisms. Patty reached its peak intensity of 40 kt near 0000 UTC 12 October. The cyclone dropped below tropical storm strength just after 1200 UTC that same day as strong vertical shear continued to remove the convection from the center. Other than a small episodic burst of relatively cold-topped convection that was quickly sheared away, Patty remained devoid of significant deep convection for about 18 hours, and it degenerated into a remnant low pressure system around 0600 UTC 13 October, when a low-level center could no longer be identified.
b. Meteorological Statistics
Observations in Patty (Figs 2 and 3, to be added in the final rendition) 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 were also used. Various microwave instruments, most notably the AMSUB unit, were also useful in tracking the center of Patty, as was Advanced Scatterometer (ASCAT) data.
The peak intensity of Patty is estimated to be 40 kt, and is based on Dvorak estimates ranging from 2.5 to 3.0. Using a shear pattern, it is possible to assign a 40 kt peak intensity to Patty around 0000 UTC 12 October, when the satellite presentation and convective vigor was most prominent. It should be noted that the Dvorak estimates escalated back to the low end of tropical storm strength in conjunction with one final convective burst which occurred shortly before 0000 UTC 13 October. While this burst generated cloud tops of -70 to -80C at a distance relatively close to the cyclone center, convection had diminished several hours before the burst began. In addition, the burst only appeared to last for about three hours, and the convection associated with this burst was rather elongated. Thus, the final best track of the storm does not show Patty regaining tropical storm strength.
c. Casualty and Damage Statistics
Despite its close proximity to the Bahamas, there were no reports of casualty or damages, as strong shear kept most of the convection downstream of the center, and with it, all of the strong wind and heavy rains.
d. Forecast and Warning Critique
The formation of Patty was not anticipated. The incipient disturbance was first mentioned about 96 hours prior to genesis. At the time, the disturbance was given a "low" (10%) chance of becoming a tropical cyclone within 48 hours. Probabilities remained in that category until genesis occurred.
Since Patty was a short-lived cyclone, there is no way to verify the track and intensity forecasts issued for the storm.
No watches or warnings were required with Patty, as westerly shear kept all of the tropical storm force winds well east of the low-level center.
Infrared satellite image of Patty at peak intensity.
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