i was watching an accuweather pundit the other night make an argument: 'look at the nhc definition of a tropical depression: a closed rotary warm-core circulation over warm waters with winds below 34kt. it doesn't say anything about thunderstorms.' the criteria i keep returning to is td 4 from 2000... a very tiny but tight low-level swirl that emerged from a complex east of florida... that often had one tiny thunderstorm sitting on its inner band. i would argue that td 10 has been a tropical depression all along, as it has met the requirements assigned by the nhc since august 12-13. after watching irene traverse the atlantic for days as a sheared system, with the center exposed more than covered.. i'd say the very similar td 10 has been the same type of system. x td 10 has also taken a track that is bringing it very near the ne caribbean... recon discovering a tropical depression this afternoon might require immediate watches.
the nhc needs to come up with a more consistent policy towards what constitutes a tropical depression. they have a definition with no minimum threshold, randomly add other criteria, and often choose to ignore very plain evidence with sheared systems. because they are inherently hard to forecast and often unstable, nhc probably ignores them as much as possible to keep their verification stats up. if you don't issue a forecast... it can't be wrong. it's one of the biggest cop-outs in weather forecasting.
HF 1328z18august