Weather 101: Tropical Investigation (INVEST)

Weather 101

We are just past the climatological peek of hurricane season which occurred September 10/11. Since we still have a few months of warm ocean water left, our weather team decided to go through a break down of all the types of tropical classifications used by the National Hurricane Center.

To start off our series on tropical classifications, we will explore what an invest or disturbance is.

Most tropical disturbances start off as a tropical wave or simply a wave of low pressure in the tropical latitudes. A lot of these waves will often develop off the west coast of Africa before moving westward into the Atlantic basin.

Tropical waves become an invest when the National Hurricane Center (NHC) wants to start examining the area of disorganized thunderstorms for potential tropical development. Invest is simply shorthand for investigation.

Invest 90L from Thursday September 17, 2020 which Became Tropical Storm Beta

Once the area of the potential development is declared an invest, the NHC can start collecting data and run model guidance on it.

Invests are numbered 90 through 99. Once 99 has been reached, the NHC restarts the numbering at 90. In addition to a number, the disturbances also receive a letter corresponding to which part of the ocean basin they originate in. The NHC issues warnings and advisories for two basins.

  • Invests in the North Atlantic are given a L
  • Invests in the Northeastern Pacific are given a E
  • Invests in the North Central Pacific are given a C (These warnings are issued by the Central Pacific Hurricane Center in Honolulu, Hawaii)

The NHC rates tropical disturbances in a low, med, and high confidence of development for 2 and 5 day outlooks.

The invest is symbolized by an X that is either yellow, orange, or red depending on the confidence of formation. The confidence is indicated in a percentage beside the center of circulation.

  • Yellow = low confidence (<40%)
  • Orange = medium confidence (40-60%)
  • Red = high confidence (>60%)
Invest 98L Off the Coast of Africa

Once a disturbance reaches sustained winds of 38 mph or less and has a closed low level circulation, it is then given the title of a “tropical depression.” We will explore this classification in a later episode of Weather 101.

Copyright 2020 Nexstar Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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