Relatively cold dense air sometimes flows from the Bay of Campeche (Gulf of Mexico), through the Chivela Pass, into Gulf of Tehuantepec on the Pacific side of the Sierra Madres. Near the coast, these winds can reach 25 m/s (strong enough to sandblast the paint off of ships); however, the scatterometer observations do not capture the near shore winds because the land mask extends 25 to 50 km offshore.

The first animation begins during a mature event. Near the end of the animation Hurricane Marco begins for form in the Caribbean Sea, weakening the gap flow. In the second animation, the hurricane strengthens, causing the gap flow to turn to the left and travel from the Pacific through the gap near the Gulf of Papagayo (by Lake Nicaragua), and enter the Caribbean Sea.

• Nov. 8 - 15, 1996
• Nov. 15 - 22, 1996

If you have difficulties running the animations (e.g., they seem jumpy) see the advice given on our main wind animations page.

It is difficult to follow the rapidly evolving wind trajectories in the moving vector animations. Wind trajectories trace the motion of air parcels over time. In contrast, streamlines show where air parcels would move if the wind field did not evolve. The background wind vectors represent the winds on the day listed at the top of the image. Streamlines would be parallel these winds; however, trajectories respond to winds from later days and need not match the intial wind field. In fact, trajectories would match streamlines only when the wind do not change with time. In this example, the wind field is far from constant: the influence of the hurricane on the trajectories is evident before the hurricane is seen in the background wind vectors. The first arrowhead on the trajectories represents 3 hours travel, and every layer arrowhead indicates an additional 24 hours. Air parcels are traced from seven locations on the Pacific Ocean side of the Isthmus of Tehuantepec. Initially the trajectories curve to the right as would be expected in the Northern Hemisphere (in the absence of pressure gradients). As the influence of Hurricane Marco is felt, the winds gradually turn to the left. As the influence of the hurricane weakens (it moves away) the trajectories again turn to the right.

• Parcel Trajectories (Nov. 8 - 23, 1996)