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Tropical Depression One-Q Discussion Number 1

Wiki-Hurricanes Forecast Center

6:00 PM AST Sat Mar 23 2019

High-resolution visible imagery from this afternoon indicates that a well-defined low-level circulation has developed approximately 280 miles northeast of Serra, Brazil within a trough of low-pressure extending from Brasilia out into the South Atlantic of sufficient organization to be considered a tropical depression. The center could be readily identified as a vortex of low-level cumuli which has since moved under an area of quickly developing convection with cloud tops cooler than -80C. Tenative banding features are developing in the storm's eastern semicircle, though without recent microwave data it is difficutl to diagnose the storm's internal structure. We have no recent scatterometer data, with the latest being a 00:30 UTC observation of 15 kt winds. Given the robust convection developing and the well-defined ciruclation evident, the initial intensity has been set at an uncertain 25 kt.

One-Q is currently tracking slowly towards the southeast at 135/5 kt in an area of weak steering currents. Conditions are abnormally favorable for tropical intensification in the South Atlantic. Sea surface temperatures off the coast of Brazil range from 28-29C and the vertical thermodynamic profile is well-suited for convective initiation. The system is also well-positioned under an upper-level anticyclone with low shear conditions prevailing. One-Q is expected to gradually intensify in these favorable conditions over the next three days. The later-term intensity forecast for One-Q is highly contingent on its future path which is currently split into two camps in model guidance, with one scenario keeping the system close to the Brazilian coast and perhaps bringing it inland sometime mid-next week with the other scenario capturing One-Q with a trough and bringing it out to sea. In one case the system's intensity will be tempered by land mass, while an increase in wind shear induced by an amplifying trough would eventually cause the system to shear out by day 5. Given the steering layer weakness carved by a disturbance to the southeast, the out-to-sea solution is being favored at this time. The current intensity forecast shows gradual intensification in the next 3 days followed by weakening thereafter.


FORECAST MAX WINDS

INIT 23/2100Z 25 KT 30 MPH

12H 24/0600Z 25 KT 30 MPH

24H 24/1800Z 30 KT 35 MPH

36H 25/0600Z 35 KT 40 MPH

48H 25/1800Z 40 KT 45 MPH

72H 26/1800Z 40 KT 45 MPH

96H 27/1800Z 35 KT 40 MPH

120H 28/1800Z 30 KT 35 MPH...POST-TROP/REMNT LOW