The term "invest" is used every hurricane season in the Atlantic and the Eastern and Central Pacific basins, accompanied by a number from 90 to 99 and either the suffix "L," "E" or "C," respectively.
We know this sounds confusing, but we’re here to break it down for you.
An invest is simply a naming convention used by the National Hurricane Center in Miami, the Central Pacific Hurricane Center in Honolulu, Hawaii, and the U.S. Joint Typhoon Warning Center in Pearl Harbor, Hawaii, to identify areas they are investigating for possible development into a tropical depression or tropical storm within the next five days.
In the Atlantic, these systems are tagged as Invest 90L, Invest 91L, all the way up to Invest 99L, and then it starts back at 90L and repeats. The only difference in the Eastern Pacific is that they are labeled with an "E" instead of an "L," so Invest 90E, Invest 91E, and so on. Similarly, in the Central Pacific, they are Invest 90C, Invest 91C, up through Invest 99C, and then back to 90C.
The NHC, CPHC, and JTWC use this naming convention because once a system is dubbed an invest, a collection of specialized datasets and computer forecast model guidance can begin in that area of disturbed weather. These computer models simulate the system’s projected track possibilities and predict its future intensity.
You might be wondering why the designation of invests only utilizes the numbers from 90 to 99.
According to Dennis Feltgen, communications and public affairs officer at the NHC, the numbers from 1 to 49 are used for tropical and subtropical depressions, 50 to 79 are reserved for other tropical cyclone forecast centers around the world and 80 to 89 are applied only for testing or training purposes.
Additionally, you may find it odd that Atlantic invests don’t use the suffix "A." This is because the Atlantic drew the short straw.
Per NOAA’s National Hurricane Operations Plan, the JTWC has that suffix reserved for the other "A" ocean basin: the Arabian Sea in the northern Indian Ocean.
Four times daily at 2 a.m./p.m. and 8 a.m./p.m. Eastern daylight time, the NHC produces a five-day Tropical Weather Outlook showing potential areas of future tropical development in the Atlantic and Eastern Pacific. Not all of these areas are tagged as invests, however.
In fact, just because a system is deemed an invest doesn’t necessarily mean it is likely to develop into a tropical depression or tropical storm. It’s just the NHC’s way of obtaining more information on areas it is watching in the Atlantic and Eastern Pacific.
"Particularly near the beginning of the (hurricane) season, it’s not uncommon for NHC to create one or more invests solely to test data flow or model processing scripts," Feltgen said. "The Tropical Weather Outlook should always be consulted to determine the significance or potential threat of an invest disturbance."