Tropical Cyclone Report (TCR): Tropical Storm Joyce
Tropical Cyclone Report
Tropical Storm Joyce (AL102012)
22-24 August 2012
Joyce was a brief tropical storm that formed over the central Atlantic and quickly succumbed to strong vertical shear.
a. Synoptic History
A tropical wave moved off the coast of Africa late on 18 August, and is believed to have been the precursor to Joyce. This wave trailed immediately behind the one that would spawn Hurricane Isaac. The associated shower activity showed signs of organization as the wave moved quickly westward across the eastern Atlantic, although satellite pictures during the following few days suggested that the strongest of the associated convection was located to the west of the wave axis, probably as a result of moderate easterly shear which was also evident in the overall outflow pattern; this sort of shear pattern is not uncommon in the deep tropics in the Atlantic basin, particularly with easterly waves that propagate off Africa and move across the Atlantic east of 35W, since such systems are generally closer to the center of the Bermuda-Azores ridge. Nevertheless, satellite and scatterometer data indicated that the wave had a well-defined lower- to middle- tropospheric circulation, and this feature quickly showed signs of closing off at the surface. A low pressure area developed within the wave on 20 August. Organization continued, and it is assumed that the system acquired enough organization to be considered a tropical depression near 1200 UTC 22 August, while centered approximately 900 miles west-southwest of the Cape Verde Islands. 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 in the final rendition). The best track positions and intensities are listed in Table 1 (to be added in the final rendition) An upper low over the central Atlantic, the same one that was initially responsible for shearing Isaac, produced strong southerly shear over the tropical cyclone, which prevented significant development. Under the influence of a synoptic scale ridge to the north, the depression moved generally west-northwestward. Although the shear never relaxed, the depression was able to generate a persistent burst of convection which led to the formation of a tropical storm around 1200 UTC the next day.
Joyce began to weaken almost immediately after becoming a tropical storm, as southerly shear increased over the cyclone as the upper low strengthened and moved east. Joyce turned northwestward and weakened to a tropical depression around 0000 UTC 24 August as the deep convection sputtered. Lacking any significant convection near its center, Joyce degenerated into an elongated trough at approximately 1200 UTC, at which time microwave, satellite, and scatterometer ambiguities indicated that the low-level center was no longer closed. The remnant circulation lost its identity shortly after 1800 UTC that day.
b. Meteorological Statistics
Observations in Tropical Storm Joyce include include the Dvorak-based satellite intensity technique, which were introduced by the Tropical Analysis and Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB).
Joyce's peak intensity of 35 kt near 1200 UTC 23 August is based on unanimous Dvorak estimates from TAFB and SAB, when they reached 2.5 near 1200 UTC. This was also based on an AMSUB microwave overpass at 1230 UTC 23 August, which showed the center tucked within the southern edge of a robust central dense overcast (CDO). Geostationary satellite images were used to authenticate the peak intensity as well, at which time Joyce was exhibiting a curved band pattern.
There were no ship reports of tropical storm force winds in association with Joyce.
c. Casualty and Damage Statistics
No reports of damage or casualties have been received in association with Joyce.
d. Forecast and Warning Critique
The genesis of Joyce was fairly well anticipated. The tropical wave that would spawn Joyce was first introduced in the Tropical Weather Outlook (TWO) at 0600 UTC 20 August, and was assigned a "low" (10%) chance of development. Genesis forecasts reached the "high" probability (60%) about 48 hours later, approximately 12 hours prior to genesis.
Since Joyce lasted for only 48 hours, it is impossible to meaningfully verify any of the forecasts that were issued on the storm.
Visible satellite photo of Joyce at its peak intensity at 1200 UTC 23 August.