The Corn Islands sit in the Caribbean, so their climate follows Caribbean patterns rather than the Pacific-facing dry season that governs most of Nicaragua's tourism calendar. The driest months are generally March through May, and again in September and October — these are the best times for diving visibility and calm seas for the panga crossing to Little Corn.
The wettest months are November through January, with heavy rain and rougher seas possible. The La Costeña flights and panga crossings can be delayed or cancelled in bad weather, which is worth factoring into your plans if you have a tight schedule.
Lobster season runs from October through June, so if you are coming specifically for the seafood, avoid the July–September period when lobster is officially off the menu. Water temperatures are warm year-round, rarely dropping below 26°C, making the diving comfortable in any season.