Tropical Storm Arlene develops in the Bay of Campeche but a threat to Mexico only
[5:45 PM EDT update:]
Tropical Storm Arlene has risen in intensity his this morning, and is now at 60 mph, with a pressure down to 996 mb. The Mexican government has issued hurricane warnings, meaning that winds are exceeded to reach, or exceed, 74 mph within 36 hours. I personally believe that Arlene may reach hurricane status before landfall in the morning, but a 70 mph peak seems more likely at this point. Regardless, very heavy rains are expected to help end Mexico's drought. I will have a full blog entry regarding the latest update on what could be Hurricane Arlene and my July 2011 outlook for the Atlantic basin.
[End of update]
Arlene, the first tropical storm of the 2011 Atlantic hurricane season, is now upon us on this early Wednesday morning. Yesterday, hurricane hunters flew into what was previously Invest 95L, and found a well-defined center of circulation, a closed low pressure area, and maximum sustained winds of 40-45 mph. Thus, the National Hurricane Center upgraded this to a tropical storm. Current maximum sustained winds are thought to be around 40 mph, with a minimal central pressure of 1002 mb. However, given Arlene's satellite appearance, as well as measurable winds between 45-50 mph from an unscheduled recon flight, I believe Arlene is pushing 50 mph at this time. The main problem with the system yesterday was the lack of deep convection of the western side of the system, due to the presence of an upper trough in the western Gulf of Mexico bringing dry air and wind shear upon the system. Since then, wind shear has lowered, and dry air has dissipated, allowing for a favorable environment for strengthening. Arlene is currently moving to the WNW at a slow pace, between 5-10 mph. A turn to the west is expected later on today as the Texas/Mexico ridge and the ridge of high pressure in the Atlantic build back in across the Gulf states of the USA. Eventually, the system should bend back WSW before landfall in central Mexico tomorrow. Accordingly, the National Hurricane Center has placed tropical storm warnings for:
* THE COAST OF NORTHEASTERN MEXICO FROM BARRA DE NAUTLA NORTHWARD TO BAHIA ALGODONES
Figure 1. Surface Wind field and current TS warnings for Arlene made by the National Hurricane Center.
Due to Arlene's monsoonal origins, its take a while for systems like this to spin up. But once they do, they tend to strengthen rapidly. Fortunately for Mexico, Arlene only has about 24-36 hours before landfall, which will not give it much time to become anything more than a tropical storm. A hurricane is not out of the question at this time, since the cyclonically curved coast of the Bay of Campeche tends to spin up systems quickly, like Hermine and Karl of last year took advantage of. The official National Hurricane Center forecast has a peak of 60 mph. I agree that Arlene could peak here, but I would go a little higher, near 65-70 mph, on peak intensity given that it is probably pushing 45-50 mph at this time, and has all day to strengthen. The NHC is giving this system a 10% chance at hurricane status, but I think these chances are way higher, near 30%, especially if it takes advantage of the higher Ocean Heat values it is passing under, and it spins up quicker because of the topography of the Bay of Campeche. Regardless, as I have already mentioned, I forecast a peak of 65-70 mph. This may go up or down throughout the day, but I feel confident in 65-70 mph.
Figure 2. The National Hurricane Center's intensity forecast for tropical storm Arlene.
There are not many things playing in Arlene's track forecast, making it relatively easy to forecast. As I wrote at the top of this blog, Arlene is currently moving WNW between 5-10 mph. However, a turn to the west is expected today as high pressure takes control of the USA, ruling out landfall there. If this system were able to strengthen more, it is possible a more northerly track could occur, but it would still be making landfall on northern Mexico. At this time, it is not expected to get terribly strong, so a landfall in central Mexico is a good bet. Before it makes landfall, as high pressure really begins to dominate, a turn to the WSW will occur, so residents in the Tampico area especially need to be prepared for tropical storm force winds and torrential downpours. The current National Hurricane Center track follows exactly what I just wrote above, taking it WNW to W to WSW up until landfall. The impacts to Mexico are expected to be just as they are to Tampico - flooding rains, strong winds, and even the possibility of landslides and mudslides. A total of 5-10" is being predicted in mainland Mexico, which will no doubt cause trouble just as Alex did to northern Mexico a year ago. I urge people to listen to their forecasting agency, or the National Hurricane Center, for updates on this system.
Figure 3. The National Hurricane Center's forecast track for tropical storm Arlene.
My next update will be in the morning, probably before 10AM, with the current information on Arlene, along with current conditions in Mexico.