It's not the heat but the humidity that gets you, at least that's what they say. Really, both are important, what you need is a sensor that combines humidity and temperature readings. How about this Honeywell HumidIcon Digital Humidity/Temperature Sensor?

The HIH6130 is a digital output-type relative humidity (RH) and temperature sensor combined in the same package. This allows the RH measurement to be temperature compensated and provides a second, standalone temperature sensor output.

This breakout board gives you standard 0.1" spaced headers for each of the pins on this SOIC package, making it a lot easier to prototype your next humidity-sensing application. Communication with the HIH6130 is easily achieved over I2C using libraries like "Wire.h"

Features:
  - Operating Voltage: 2.3-5.5v
  - Compensated humidity range: 10-90% RH
  - Compensated temp. range 5-50°C
  - True temperature-compensated digital I2C output
  - Wide operating temperature range allows for use in many applications