Wave Bringing Heavy Rain to Central America

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A tropical wave we have been tracking for days has became much better organized over the past 24 hours. Thunderstorms increased in coverage and intensity across the western Caribbean. Upper-level winds relaxed, lessening the shear. As a result, good outflow was present over the thunderstorms from late Sunday into this morning.


An apparent center of this feature can be seen in the infrared satellite loop this morning just north of Honduras. The system is expected to move westward and over Belize and the Yucatan Peninsula by tonight. There is a short window of time during the day today that the system could develop into a tropical depression before it moves over land. The interaction with land will certainly hinder chances for significant development.

Even though significant tropical development is not expected, it will bring widespread heavy rainfall to parts of Central America and southern Mexico today through Tuesday. So, deadly flooding is a big concern. This feature could reorganize over the southern Bay of Campeche towards the middle of the week, but it will likely remain too far south to have any impact on the U.S.

There are no other areas of concern across the Tropical Atlantic. The Inter Tropical Convergence has been pushed very far to the south, south of 10 degrees north. Also, there is a widespread area of Saharan dust extending from the Africa coast to the Lesser Antilles. This Saharan dust will help to limit thunderstorm activity north of 10 degrees north for at least the next few days. There is a weak tropical wave near 55 west, south of 10 north. There are no other areas of concern across the tropical Atlantic at this time.

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Tropical Storm Andrea, the first named storm of the 2013 Atlantic Hurricane Season, made landfall around 5 p.m. EDT Thursday near Horseshoe Beach along the Big Bend of Florida.

Andrea continues to move northeastward this morning through eastern South Carolina. The strongest winds, which weakened considerably since landfall, are located on its southeast side. It looks like tropical storm-force sustained winds and gusts will be mainly over the water and at the immediate coast in South Carolina and will spread to the coast of southern North Carolina this morning.

There remains a possibility for isolated severe weather today, including tornadoes, northeast of the storm track near the coast of North Carolina into southeastern Virginia. There were several reports of (mainly short-lived) tornadoes that have taken down trees and power lines, including one report only 3 miles west-southwest of St. Petersburg, Fla.


The rainfall amounts of 2-4 inches today through tonight will be across the eastern Carolinas and eastern Virginia, then northeastward into southern New England with 1- to 2-inch rainfall amounts as far north as Maine.

Elsewhere, a tropical wave along 70 west has become less defined and is expected to continue to weaken. Another tropical wave between 45 and 50 west has some organization with a weak surface low and some signs of rotation. However, as this wave advances farther to the west and northwest, it will encounter stronger shear, causing the system to become less organized over the next day or two. The wave is expected to bring an increase in showers and gusty winds to the Leeward Islands and across the northern Caribbean Sunday into Monday.

Andrea

The Atlantic has its first named storm of the 2013 hurricane season: Tropical Storm Andrea.

 An Air Force hurricane hunter plane was able to locate a closed center of circulation, and found surface winds of 40 mph in the large area of thunderstorms on the east side of the center. Satellite loops show that Andrea is a lopsided storm. It's center of circulation is exposed to view, due to a large region of dry air that covers the entire Central and Western Gulf of Mexico. This dry air is from a trough of low pressure whose upper level winds are also creating moderate wind shear of 15 - 20 knots over Andrea. 

Wind shear is forecast to rise to the high range, 20 - 40 knots, by Thursday. Andrea is forecast to make landfall along the northern Gulf Coast of Florida by Thursday evening, so the system has a short window of time to intensify. Given the large amount of dry air to Andrea's west, and the forecast for increasing shear up until landfall, I expect that the strongest sustained winds Andrea could have before landfall are 50 mph. Heavy rains will be the storm's main threat, though a few isolated EF-0 tornadoes will also be possible in some of the heavier thunderstorms in Andrea's spiral bands. 

A storm surge of 2 - 4 feet is predicted for Tampa Bay northward to Apalachicola, and rip currents will be a risk for swimmers who brave the high surf. Fort Pickens, located in Gulf Islands National Seashore on a barrier island offshore from Pensacola, Florida, has been closed to visitors due to the approaching storm. A single 2-lane road vulnerable to storm surges runs to Fort Pickens. Officials want to prevent a repeat of the situation that occurred in September 2011, when Tropical Storm Lee pushed a storm surge over the road that blocked it with sand and debris, trapping numerous campers and visitors in Fort Pickens. As of 7 pm EDT, our wundermap with the storm surge layer turned on was showing storm surge levels were less than 1 foot along the Florida coast.

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AccuWeather.com meteorologists are monitoring possible tropical development for the middle of this week. Recent satellite imagery shows an area of showers and thunderstorms extending from the Yucatan Peninsula to just east of the Florida Straits. High wind shear is present in the region and will continue to inhibit development of this area over the next 24 hours, so any organization during this time should be slow to occur.

Wind shear is expected to weaken during the middle of the week and global forecasting models continue to indicate an area of broad tropical development over the central Gulf of Mexico. If this system manages to organize into a tropical storm, it would take on the name "Andrea" and be the first named storm of the Atlantic Hurricane Season.

Most computer models show that this disturbance will drift northeastward into parts of the eastern Gulf of Mexico during midweek, then move over Florida late in the week, likely bringing heavy rainfall and perhaps gusty winds to the west coat of Florida. Wind shear looks to increase across the northern Gulf of Mexico late in the week which would again work to weaken this system and prevent it from intensifying into a strong tropical system. Regardless of whether this system develops or not, with abundant tropical moisture across the region, heavy rainfall is likely across Florida this week with flooding possible, especially from Wednesday through Friday.