In the Atlantic Basin, tagging a disturbance as an Invest signals that the National Hurricane Center is formally monitoring the area and is ready to begin the collection and evaluation of meteorological data associated with the disturbed area, as well as initiate the running of computer models on it. The Invest designation also alerts cooperating agencies (government and academic groups) to begin data processing in earnest.
Officially, designation as an Invest does not mean that the tropical disturbance has an increased likelihood for development, but it is a clear sign by the NHC experts that they think the area has at least some potential.
Invests are numbered from 90 to 99, and labeled with an "L" for disturbances in the Atlantic Basin. (By comparison, an "E" is used for Invests in the eastern Pacific). Given this naming scheme for Invests, you can see that during an ‘active' year, there could be two or more "90L" Invests before the season ends. Keep in mind that over the course of a tropical season, we could see as many as 50 to 70 (or more) tropical waves over the Atlantic, although only a small proportion of those earn Invest designation.
Take this season for example: we are currently watching 96L, the sixth Invest of the season. Yet only three have become tropical cyclones: hurricanes Arthur & Bertha, and between them, Tropical Depression #2).
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