Two Minor Atlantic Threat Areas; Odile a Serious Rainfall Threat for Mexico

A tropical wave (91L) located about 600 miles west-southwest of the Cape Verde Islands is headed west-northwest at about 15 mph. Satellite images show 91L has a moderate amount of spin and heavy thunderstorm activity, and these thunderstorms are poorly organized. The disturbance is embedded in a moist air mass, has moderately warm (SSTs) of 28°C (83°F) beneath it, and is experiencing light wind shear. These conditions favor development. The 8 am EDT Wednesday run of the SHIPS model predicted that wind shear would remain light to moderate (5 - 15 knots) and the atmosphere at mid-levels of the atmosphere (between 500 - 700 mb) would remain moist this week, favoring development. All three of our three reliable computer models for predicting tropical storm formation predict development of 91L over the next five days. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 20% and 70%, respectively. A trough of low pressure expected to push off the U.S. East Coast early next week should induce a more northwesterly track for 91L next week, and the disturbance does not appear to be a long-range threat to the Lesser Antilles Islands or U.S. East Coast. It remains to be seen if 91L will be a threat to Bermuda or the Canadian Maritime Provinces late next week.


Figure 1. Visible satellite image of Invest 91L 600 miles west-southwest of the Cape Verde Islands at 8 am EDT September 10, 2014.

Bahamas disturbance 92L very disorganized
A weak area of low pressure over the Bahamas (92L) is bringing a few heavy rain showers to the islands, but this this activity is disorganized. Although wind shear is a moderate 10 - 20 knots and ocean temperatures are a very warm 30°C (86°F), the presence of dry air and cold air aloft associated with an upper level low will allow only slow development of the disturbance as it drifts westwards at 5 - 10 mph. The disturbance should move over Florida on Friday and emerge over the Gulf of Mexico on Saturday, bringing rains of 1 - 3" to much of Florida. None of the three reliable computer models for predicting tropical cyclone genesis develop the disturbance. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 10% and 20%, respectively.

Tropical Storm Odile a serious flooding threat for Mexico
In the Eastern Pacific, Tropical Storm Odile formed on Wednesday morning a few hundred miles southwest of Acapulco. Satellite loops show that Odile has an imposing area of heavy thunderstorms that are steadily organizing, and this storm represents a serious rainfall threat to the Pacific coast of Mexico. The slow-moving storm will be capable of dumping 5 - 10" of rain along the coast from Acapulco to Puerto Vallarta beginning on Thursday.


Figure 2. Predicted rainfall along the track of Odile from the 06Z (2 am EDT) September 10, 2014 run of the GFDL model. The model predicted that TD 15-E would be a strong tropical storm or Category 1 hurricane as it brushed the coast of Mexico this week, bringing widespread rains of 8 - 16" along the coast from Acapulco to Manzanillo. Image credit: NOAA/GFDL.

Moisture from Hurricane Norbert and Tropical Storm Dolly brings heavy rains to U.S.
The counter-clockwise flow of air around Hurricane Norbert, which dissipated off the coast of Mexico's Baja Peninsula over the weekend, pulled moisture from the remnants of Tropical Storm Dolly and from the tropical Eastern Pacific northwards into Northern Mexico and Southern Arizona, bringing epic rainfall amounts and severe flooding on Monday. According to Wunderground's weather historian Christopher C. Burt in his latest post, the official weather site at Phoenix’s Sky Harbor International Airport has its rainiest day in recorded history on Monday, with 3.29” falling. Moisture from Norbert also helped contribute to torrential rains that affected Northern Missouri on Tuesday night into Wednesday morning. As of 8 am EDT Wednesday, 10.54" was recorded in 12 hours in Browning, MO, with 9.61" inches falling at Chillicothe. Moisture from Norbert will spread all the way into Michigan's Upper Peninsula on Wednesday afternoon, and an Areal Flood Watch is posted there for flooding rains of 1 - 3".


Figure 3. The remnants of Hurricane Norbert lie off the coast of Baja, Mexico at 7 pm EDT September 9, 2014, in this photo taken from the International Space Station by Reid Wiseman.

WSI's Mike Ventrice has a technical post on the Atlantic hurricane outlook for the next two weeks at the WSI WeatherWise blog.

Hurricane expert Steve Gregory has a more detailed look at the tropics as well as a discussion of the record rainfall in Arizona yesterday in his latest post.

Jeff Masters