The phrase "warm seas" means oceans or bodies of water that have a higher temperature and are not cold.
Sentences with «warm seas»
He notes that last year's activity was related to very favorable upper - level winds as well as the extremely warm sea surface temperatures. (heatisonline.org)
The latter is caused by penetration of warmer sea currents and loss of albedo causing increased exposure to sunlight. (skepticalscience.com)