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The geographical boundaries for each region with their letter identifiers are:
Atlantic(L): North of the equator between N. America and Africa
East Pacific(E): North of the equator between 140W and N. America
Central Pacific(C): North of the equator between 180W and 140W longitude
West Pacific(W): North of the equator between 100E and 180E longitude
Indian Ocean:
(A) North of the equator between Africa and 77E longitude
(B) North of the equator between 77E and 100E longitude
Southern Hemisphere:
(P) South of the equator between 135E and S. America
(S) South of the equator between Africa and 135E longitude
Letter identifiers are assigned to the storm's basin of origin. If a storm passes over a basin boundary, the storm will maintain it's basin of origin letter identifier even though it has entered a new region. For example, storm "Alpha" originates in the Eastern Pacific and is assigned 01E. If it makes its way into the Central Pacific it will still maintain its number and name designation even though it is seen under the Central Pacific header.
The storm number can be an eighty series (80-89), ninety series (90-99), or a number between 1 and 50. Storms seen with a number between 80 and 89 are usually used for testing purposes only. Storms with numbers between 90 and 99 are areas that forecasters use to monitor suspect regions typically with disorganized large-scale convection that has a chance to develop into a more organized system such as a tropical depression. Storms with numbers between 1 and 50 are/were storms that reached tropical storm strength or higher.
The naming convention after the number/basin pair can be called INVEST, NONAME, or assigned name. All storms will start with an INVEST name. When the system becomes a tropical storm this name will change to either NONAME or assigned name. NONAME is assigned to storms which do not have an official assigned name yet. Assigned names are given to tropical storms according to the World Meteorological Organization (WMO). Typically, storms that form in the Indian Ocean north of the equator will have NONAME. There are a few occasions where a tropical storm name will have an INVEST or a ONE, TWO,... following the number/basin pair. This name is only temporary and typically lasts for only a couple of hours. This is caused by the timing of the position updates generated by the Automated Tropical Cyclone Forecasting (ATCF) system and when forecasters determine that the system has become a tropical storm. I know that many new members that had registered at storm2k recently dont know when someone posts about an invest what it is and how this works and that is why I am posting this explanation above.
