I have cruised that coast going the opposite direction--it's a fine
cruise.
Weather is mostly going to be affected by land: look out for Papagallos from
Nicaragua to
Guatemala, be wary of Tehuantepeckers. The local
cruising guides (Sail Sarana was just being published when I went by) do a very good job of covering the weather and other wildlife.
There's lots of neat stuff to see, some
remote places on the way (stock up on supplies when you can--your best bet is the city of David, accessed from Pedregal in
Panama: next decent grocery store going north is in Mexico).
Avoid Corinto,
Nicaragua; by all means explore the Gulf of Fonseca, and don't be afraid of crossing the bar into
Bahia del Sol in El Salvador.