Figure 3. A conceptual diagram of the Gulf Surge phenomenon. Gulf surges may be triggered by the passage of a tropical disturbance near the mouth of the Gulf or by organized convective activity that move over the Gulf from the Sierra Madre. The Gulf acts as a natural passageway for moisture (long solid black arrows) drawn into the deserts of northwest Mexico and southern Arizona and California by a semi-permanent thermal low. The increase in moisture into this region then results in greater thunderstorm activity.