There are several favorable precursor environmental conditions that must be in place (Gray 1968, 1979):

1.  Warm ocean waters (of at least 80 degrees F, roughly 26 degrees C) throughout a sufficient depth of about 150 feet (roughly 50 meters)..  Warm waters are necessary to fuel the heat engine of the tropical cyclone.

2.  An atmosphere which cools fast enough with height such that it is potentially unstable.  It is the thunderstorm activity which allows the heat stored in the ocean waters to be liberated for the tropical cyclone development.

3.  Relatively moist layers near the mid-troposphere.  Dry mid levels do not allow the continuing development of widespread thunderstorm activity.

4.  A minimum distance of at least 300 miles (about 500 km)  from the equator.

5.  A pre-existing near-surface disturbance.  Tropical cyclones cannot be generated spontaneously.
To develop, they require a weakly organized system with sizable spin and low level inflow.

6.  Low values (less than about 20 mph) of vertical wind shear between the surface and the upper troposphere.  Vertical wind
shear is the magnitude of wind change with height.  Large values of vertical wind shear prevent the creation of a tropical cyclone, or can weaken or destroy the tropical cyclone by interfering with the organization of deep convection around the cyclone center.

 
Note: Having these conditions met is necessary, but not sufficient to the development of hurricanes.  Many disturbances that appear to have favorable conditions do not develop into tropical cyclones.