Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Name | Year | Landfall | NHC Advisory Number | V(mph) | R(miles) | Saffir-Simpson Category |
| --- | --- | --- | --- | --- | --- | --- |
| Bonnie | 1998.0 | North Carolina | 31B | 115.0 | 115.0 | 3.0 |
| Earl | 1998.0 | Florida | 11 | 80.0 | 115.0 | 1.0 |
| Georges | 1998.0 | Mississippi | 51B | 105.0 | 45.0 | 2.0 |
| Bret | 1999.0 | Texas | 17 | 140.0 | 40.0 | 4.0 |
| Floyd | 1999.0 | North Carolina | 34A | 110.0 | 115.0 | 2.0 |
| Irene | 1999.0 | Florida | 9 | 75.0 | 30.0 | 1.0 |
| Lili | 2002.0 | Louisiana | 48A | 100.0 | 60.0 | 2.0 |
| Claudette | 2003.0 | Texas | 27A | 75.0 | 30.0 | 1.0 |
| Isabel | 2003.0 | North Carolina | 49A | 100.0 | 115.0 | 2.0 |
| Charley | 2004.0 | Florida | 18 | 145.0 | 30.0 | 4.0 |
| Frances | 2004.0 | Florida | 44A | 105.0 | 75.0 | 2.0 |
| Ivan | 2004.0 | Alabama | 55B | 130.0 | 105.0 | 3.0 |
| Jeanne | 2004.0 | Florida | 49B | 115.0 | 70.0 | 3.0 |
| Dennis | 2005.0 | Florida | 25B | 120.0 | 40.0 | 3.0 |
| Katrina | 2005.0 | Florida | 9 | 75.0 | 15.0 | 1.0 |
| Katrina | 2005.0 | Louisiana | 26A | 145.0 | 120.0 | 4.0 |
| Rita | 2005.0 | Texas | 26B | 120.0 | 85.0 | 3.0 |
| Wilma | 2005.0 | Florida | 36 | 125.0 | 90.0 | 3.0 |
Question:
What was the highest SaffirSimpson with an NHC advisory of 18?
Answer:
4.0