May is fabulous for Alaska ... but assuming you hit Mexican border in June or so ... this is where things may not be ideal ... Weather wise. By May Mexico and Cent. America really HEAT UP. May/June are hottest months there.

If lucky Rain may hold off until late June or even July. As I said above, heaviest rain typically falls in Aug./Sept. This varies year to year.

With clear global warming going on anything can happen and typical patterns don't always work out, less predictable.

Even in normal years rain always creates mayhem on roads/bridges in Cent. America, with global warming could be even worse. Problem in Cent. America is very few main roads going North/South, so when a main road washes out, it can be MONTHS until repaired (even years).

Mexico better in this regard. More roads, better road crews, more money.

Best months for travel in Mexico and Cent. America are October through
April. Fairly dry, slightly cooler temps (it's never truly "cool" in Cent. Am).

If you DO ride in rainy season plan to START EARLY each riding day. Typically, mornings can be clear (unless a storm blows in). Stays clear usually until Noon,
after that, anything can happen. Typically it clouds up and you can have rain anytime until after midnight. This happens almost every day. So, you typically get maybe 4 or 5 hours dry riding. Make best of it. Rain can last from an hour to 8 hours. Varies a lot.

If a storm comes in it can rain, non stop 3 days straight ... and everything can wash away. Been there, done that.

I lived in Guatemala and El Salvador off/on for 3 years, traveled quite a bit up and down through all the countries.

Remember the sub-tropical lowlands have heaviest rain, Highlands the least rain.

Good luck, ride safe!