Definition of invest:
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an unnamed tropical weather pattern "to investigate" for development into a significant (named) system. A temporary designation by the U.S. Joint Typhoon Warning Center and . Internal jargon (possibly teletype abbreviation) in the 1980's. Appears today on some tracking maps, e.g. tropical storm advisories at the . Designation, e.g.
91e, is a cyclic number (90-99) and a letter suffix for oceanic region: