On Sunday afternoon, the National Hurricane Center in Miami indicated that formation of the next Atlantic tropical system would occur soon, highlighting an 80 percent chance of development within the next two days, and a 90 percent chance by the end of the week.
While the system is showing organization and a cyclonic (counter-clockwise) swirl, it still lacks a closed center of circulation. At this time, it is considered to be a tropical disturbance or “open wave”. Once it obtains the closed center, it would be known as a tropical low.
If the tropical low has a closed center of circulation but sustained wind speeds less than 39 mph, it would be considered a tropical depression. If wind speeds are greater than 39 mph, then it would be a tropical storm, and it would receive the “I” name — in 2020, the “I” name is “Isaias”.
Nevertheless, tropical forecast models — known as “spaghetti plots” because of the individual lines on the map — indicate that potential Isaias would move west towards the Caribbean over the next several days. It remains to be seen how far west versus northwest potential Isaias would move, based on the strength and steering current from the Bermuda High pressure system to its north.
Below is additional information from the National Hurricane Center.
Tropical Weather Outlook NWS National Hurricane Center Miami FL 800 PM EDT Sun Jul 26 2020 For the North Atlantic...Caribbean Sea and the Gulf of Mexico: The National Hurricane Center has issued its final advisory on recently downgraded Tropical Depression Hanna, located inland over northeastern Mexico. Future advisories on Hanna will be issued by the NOAA Weather Prediction Center in College Park, Maryland. 1. Shower activity is becoming a little better organized in association with a broad area of low pressure located over the central tropical Atlantic about midway between the coast of Africa and the Lesser Antilles. Environmental conditions are expected to become increasingly conducive for development of this system, and a tropical depression or tropical storm is likely to form within the next day or two while moving westward to west-northwestward at 15 to 20 mph. This system is expected to begin affecting portions of the Lesser Antilles on Wednesday or Wednesday night, and interests on those islands should continue to monitor its progress. * Formation chance through 48 hours...high...80 percent. * Formation chance through 5 days...high...90 percent. Public Advisories on Hanna will be issued by the Weather Prediction Center under AWIPS header TCPAT3, WMO header WTNT33 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. Forecaster Berg