Tropical Cyclone Twenty One (21S) Expected to Intensify – April 8th, 201311.1S 59.0E
Tropical Cyclone Twenty One (TC 21S) will continue to track west-southwestward through TAU 48 under the influence of the deep layered sub-tropical ridge (STR) to the south.
A gradual decrease in vertical wind shear (VWS) and fair outflow will allow for intensification. Additionally, a pool of higher ocean heat content located along the forecast track will aid in this intensification. After TAU 72, a deep layer mid-latitude trough will move in from the west and begin to reorient the STR in the north-south direction, allowing for TC 21S to turn poleward.
The forecast calls for a peak intensity of 95 knots by TAU 96. Though dynamical model guidance is in generally good agreement with the poleward deflection in the extended forecast, the timing and sharpness in the deflection are still unclear. This is further evidenced by increasing spread noted in ensemble model products. There is high confidence in the three day forecast, but low confidence in the extended portion.