What does the letter L stand for on a hurricane tracking map?

Remnant low.

Explanation:

If only an L is displayed, then the system is forecast to be a remnant low. The letter inside the dot indicates the NHC's forecast intensity for that time:

D: Tropical Depression – wind speed less than 39 MPH

S: Tropical Storm – wind speed between 39 MPH and 73 MPH

H: Hurricane – wind speed between 74 MPH and 110 MPH

M: Major Hurricane – wind speed greater than 110 MPH

Source: National Hurricane Center.

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