Average 20 year old weather nerd. Plymouth State University Meteorology, Class of 2018. Interning this summer at NWS Boston.
By: MAweatherboy1 , 10:50 PM GMT on April 08, 2013
After a lengthy stretch of quite in the global tropics, there has been one tropical cyclone active for the past few days, Cyclone 21S in the Southern Indian Ocean, which has been officially named as Imelda. As of the 5PM EDT advisory from the Joint Typhoon Warning Center, Imelda is currently located about 755 nautical miles NE of La Reunion island, and is moving west at 9kts. The system's maximum 1 minute sustained winds are estimated to be 45kts by JTWC, or about 50mph. Persistent vertical wind shear over the past few days did not let up as quickly as anticipated over the system, keeping the center frequently exposed or just on the eastern edge of the convection. Now, however, shear is relaxing over the cyclone, and the center is moving directly under the central dense overcast (CDO) that the system has developed.
Figure 1: Cyclone Imelda, showing the system's CDO with deep convection.
Forecast for Imelda
Cyclone Imelda has been, and continues to be, steered W and WSW by a subtropical ridge, and this will remain the dominant steering force for the next 36 hours or so. After that time, the steering ridge will be weakened by an approaching mid-latitude trough, causing a southerly turn of the cyclone, and eventually a more SSE/SE motion. Regarding intensity, steady strengthening is likely for the next 24-36 hours as wind shear continues to abate and the system develops a better defined inner core. After this time, between about 36 and 60 hours out, there will be an opportunity for the cyclone to rapidly intensify as environmental conditions become more conducive for a stronger cyclone. The Joint Typhoon Warning Center forecasts a peak intensity of 95kts, or about 110mph, making Imelda a high end Category 2 hurricane equivalent on the Saffir Simpson Scale. They forecast the system to turn south before it can impact the Reunion Islands.
Figure 2: Official JTWC forecast of Imelda.
My forecast (not official of course) is shown in Figure 3. I forecast a slightly more westward path than JTWC as I think the steering ridge will be a little slower to break down than they do. My intensity forecast is a bit higher than JTWC's as I forecast somewhat more rapid intensification than they do in the 36-60 hour range. It should also be noted that Dvorak ADT numbers are approaching 4.0, which would indicate Imelda is considerably stronger than the 45kts JTWC has stated. While these are likely overdone, it is possible Imelda's current intensity is closer to 50kts, which may make the final peak intensity a little higher than what JTWC has listed.
This graphic does not show my forecast peak intensity as I believe it will occur between the second and third lines, with the storm topping out at around 115mph. Regarding land impacts, the only area that may be at risk are the Reunion Islands. Right now, it appears Imelda will pass far enough east of there to prevent significant impacts, but this could change if the track shifts west. Residents there should stay alert of the situation since Imelda will likely be a powerful cyclone when it is at that latitude. I will provide updates in the comment section as necessary.
Thank you for reading, and I hope you have a great week!
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