Small but Mighty: Shallow Rotating Marine Cell and NTDA

Was great to see the NTDA in action for marine areas! One particular shallow area of cells was approaching coastal Mississippi within the Mississippi Sound (generally south of Bay Saint Louis to Gulfport, MS. While some minor adjustments were necessary to allow NTDA to display for such weak rotational couplets (dropping NTDA probabilities down to around 10% was helpful in this specific case), there was rather consistent tracking with one small area of rotation.

KLIX 0.5 SRM (user defined SMV of 140ยบ @ 21kt) at 2159Z 5/18/21.

Definitely small, but mighty. These small areas of rotation not rooted to a deeper mesocyclone can easily drop weak waterspouts in tropical environments (characterized by deep moisture and very low LCL heights on average). It was nice to see NTDA tracking this cell much more consistently than anticipated, with occasional peaks of higher probability reaching as high as 36.3% (as pictured above). A Special Marine Warning went in effect around this time to mention the potential for waterspouts as this cell neared land, but dissipated before making landfall. A great example at where NTDA can easily act as a warning nudger in low-end rotational velocity cases.

– Dusty Davis