How about set-based approach:

SET DATEFIRST 1

;WITH days(Date) AS

(

--Get 13th of this month

SELECT CAST(CAST(YEAR(GETDATE()) AS VARCHAR(4)) + '-' + CAST(MONTH(GETDATE()) AS VARCHAR(2)) + '-13' AS DATETIME)

UNION ALL

--Get 13th of next months

SELECT DATEADD(MONTH, 1, Date) FROM days

)

SELECT TOP 1 * FROM days WHERE DATEPART(dw, Date) = 5 AND Date > GETDATE()