user: Question: What was the highest SaffirSimpson with an NHC advisory of 18?
Columns: ['Name', 'Year', 'Landfall', 'NHC Advisory Number', 'V(mph)', 'R(miles)', 'Saffir-Simpson Category']
Types: ['text', 'real', 'text', 'text', 'real', 'real', 'real']
Sample row: ['Bonnie', 1998.0, 'North Carolina', '31B', 115.0, 115.0, 3.0]
SQL:

assistant: SELECT MAX("Saffir-Simpson Category") FROM "Table" WHERE "NHC Advisory Number" = '18';