From Tolkien Gateway

Súlimë (Gwaeron in Sindarin) was the third month of the year in the King's Reckoning and the Stewards' Reckoning, and followed the month Nénimë. In the King's Reckoning it preceded the month Víressë while in the Stewards' Reckoning it preceded the feast-day of Tuilérë. In both calendars, Súlimë was 30 days long, lasting from the 62nd through the 91st days of the year. In the New Reckoning it was the last month of the year, preceding its Mettarë.

Súlimë in the Kings' and Stewards' Reckoning corresponded to Rethe in the Shire Calendar (approximately modern 21 February through 22 March).[1]