Since you didn't specify, I assume the MP3 files are in the current directory, and the files should go to the default FTP directory. You should be able to do something like this:
@echo off
setlocal enabledelayedexpansion
set FTPHost=myftphost.com
set FTPUser=myusername
set FTPPass=mypassword
set MonthNum=%date:~4,2%
set DayNum=%date:~7,2%
set Loop=1
for %%a in (Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec) do (
if !MonthNum! equ !Loop! set Month=%%a
set /a Loop+=1
)
set File=%Month%%DayNum%.mp3
echo %FTPUser%>cmds.ftp
echo %FTPPass%>>cmds.ftp
echo bin>>cmds.ftp
echo put %File% rw.mp3>>cmds.ftp
echo quit>>cmds.ftp
ftp -v -s:cmds.ftp %FTPHost%
echo Done transferring %File%