Helene slowly intensifying; Lane threatens Mexico

Tropical Storm Helene continues to be a very large and disorganized system. However, visible satellite imagery from this morning is now showing a slow improvement in the organization of the low-level spiral bands, and the amount and intensity of the thunderstorm activity near Helene's core is increasing. Given that the storm is over warm 27-28C waters and the shear is a low 5-10 knots, I expect Helene will slowly intensify into a hurricane by Sunday. The dry air to Helene's north and west is farther away and more dilute, so should not inhibit intensification significantly.

The computer track models still have a wide spread in the long-range track for Helene, but all of them take the storm north of the Lesser Antilles. Helene may be a threat to Bermuda and the U.S. East Coast late next week, but the odds of a strike on the U.S. are less than 10%. History shows that the large majority of tropical storms that form in this part of the Atlantic end up recurving. A very strong trough of low pressure is expected to push off the East Coast by Wednesday, and this trough should be able to pull Helene northwards and recurve the storm harmlessly out to sea.


Figure 1. Latest satellite image of Helene, updated every half hour.

Gordon on the decline
Hurricane Gordon, the first major hurricane of the season, is a major hurricane no longer. Strong upper-level winds from the west have eroded the northwest side of the storm, and the once prominent eye is now gone. About 20 knots of wind shear is now affecting the storm, and this shear is expected to increase and the waters underneath it cool over the next few days. Gordon is headed northward out to sea, and is not a threat to land.

Tropical Storm Lane nears hurricane strength
Tropical Storm Lane continues to intensify just off the Mexican Pacific Ocean coast near Puerto Vallarta. Animations of microwave satellite images show that Lane is moving parallel to the coast, about 60 miles offshore, remarkably close to the track of Hurricane John earlier this month. Lane is over warm waters and under light shear, and and has the potential to become a hurricane later today. The only inhibiting factor for intensification might be the storm's close proximity to land. Lane will be drawing in dry continental air from mainland Mexico that might slow down the intensification process. Hurricane John was able to intensify into a Category 4 hurricane under virtually the same conditions, but Lane is a much smaller storm, and might be more seriously impacted by interaction with land. If Lane can avoid passing too close to land areas, she may have enough time to intensify into a Category 2 hurricane before landfall. The people of Baja, who are still cleaning up the damage and repairing the roads washed out by Hurricane John, are probably not too happy to see Lane approaching on Cabo San Lucas radar.

Moisture from Lane could potentially reach southern Arizona and New Mexico by Wednesday and cause flooding concerns there.

The rest of the tropical Atlantic
Shower activity has increased over the extreme southwest Caribbean off the coast of Panama. However, the area affected is small and likely to move ashore over Nicaragua before any development can occur. A strong tropical wave with plenty of spin and heavy thunderstorm activity has emerged from the coast of Africa this morning. This wave is over warm waters, and wind shear is a modest 10-20 knots. This wave has the potential for some slow development over the next few days as it moves over or just south of the Cape Verde Islands. Tropical waves that emerge this far north usually end up recurving out to sea.

Remainder of hurricane season outlook
I'll post my outlook for the remainder of hurricane season this afternoon by 4pm EDT.

Jeff Masters