My fluorescent lights work fine in the winter when the humidity relatively low... but, when the summer comes and we get high humidty... they do not work... sometimes the work sometimes they don't... if I turn them on and leave them for sometime... they eventually turn on... How do I fix this problem?

Any fluorescent light fixture needs to be grounded properly, one for safety reasons, and, two, to operate properly.

I suspect the fixture is not grounded that is causing your problem, the humiditiy being the indicator.

The lamp starts by using the capacitance that exists between the lamp glass wall and a metal grounded surface.

Check the wiring feeding the fixture. If you have a green or bare ground wire, be sure it is connected the metal frame of the fixture using a machine threaded screw.

Test the ground wire to be sure it is grounded by using a voltage tester and measure 120 volts across the black wire and the ground.

If you have BX cable, the metal sheathing is the grounding conductor, and the connector's locknut must be tight to dig into the paint on the fixture for proper ground connection. BX is popular for bad grounds, as the connections rely on every clamp and connector in the circuit to be perfectly tight.

If opening the fixture to work on the wiring, and possibly needing to open other outlet and junction boxes is beyond your capabilities, you may need to call in an electrician to do the troubleshooting and repairs.

Yay, TK is back!

There is a problem with fluorescent lights that most people do not recognize. Dirty bulbs and/or dirty fixtures will cause hard starting, especially in humid conditions. Take out the bulbs and clean them with window cleaner. Clean the interior of the fixture with the same stuff, (MAKE CERTAIN IT IS TURNED OFF!) let it dry and reassemble. Things should work fine from then on. If they don't, you probably have old bulbs, wrong wattage or wrong type bulbs for the ballast, or a bad ballast (in that order). There are other possibilities, tkrussel covered another one, and the rest you don't need to know. Sorry I can't find the link to give the whole nine yards.

Corroded sockets are one other problem.