By PDC’s Senior Weather
Specialist Glenn James
Current Tropical Cyclones:
Tropical Cyclone 05S (Darian)…is located approximately 934 NM southeast of Diego Garcia
Northwest and Southwest Pacific Ocean, North and South Indian Oceans, and Arabian Sea:
South Indian Ocean
Tropical Cyclone 05S (Darian)
According to JTWC Warning number 18, sustained winds were 110 knots, with gusts to 135 knots.
Over the past 12 hours, tropical cyclone 05S (Darian) has weakened fairly significantly, as it drifted slowly towards the southeast over an area of strong oceanic upwelling. Over the past six hours, the system has lost its previously well-defined eye in the enhanced infrared (eir) imagery, though a strong microwave eye feature remains present in the most recent image.
Deep convection has started to redevelop over the past couple of hours, with cold cloud tops developing near the assessed center. The microwave imagery indicates the eyewall is open on the northeast side, and high-resolution model fields suggest the presence of a wedge of dry air in the northeast sector which when combined with the much cooler sea surface temperatures to the north, would support a weaker wind field on that side of the system.
The overall environment is favorable, with the system now moving away from the upwelling and into a warm sea surface temperature tongue. In the upper-levels, shear is moderate and outflow is restricted on to a poleward channel only, now that a weak upper-level low has developed just to the west of the system, cutting off the westward and equatorward outflow that was present yesterday. TC 05S is moving southeastward along the southwestern side of a near-equatorial ridge.
Through the first 12 hours of the forecast, TC Darian will continue to track southeastward at a fair clip, along the strong steering gradient on the southwest side of the ridge. By 24 hours, TC 05S will slam on the brakes as the ridge quickly moves west and weakens, putting 05S into a weak steering environment. The system will slowly turn to the south then southwest through 48 hours as the steering pattern shifts to the building subtropical ridge to the south.
After 48 hours the system will accelerate southwestward through 96 hours. By 120 hours the ridge will shift to the north and take up position to the east of TC 05S, which will lead the system to begin a poleward turn by the end of the forecast period.
Over the next 24 hours the system will continue to slowly weaken due to northerly shear and intrusion of dry mid-level air from the north. The weakening trend is forecast to be arrested after 24 hours as the system moves over the warmest portion of the warm sea surface temperature tongue and shear relaxes somewhat.
But the arrested weakening will be short-lived, and after tau 48 the system will begin to rapidly weaken as it moves into steadily cooler waters as it continues moving southwestward. By 96 hours or slightly earlier, the system will be over much cooler waters, will be moving poleward of the subtropical ridge, and will be increasingly engulfed by a dry air mass, marking the start of subtropical transition.