September 4, 2009
Erika Now a Remnant Low Over Puerto Rico and Virgin Islands
Hurricane Season 2009: Tropical Storm Erika (Atlantic)
Erika has had a difficult holding together as a tropical storm, and deteriorating conditions have now diminished her status to a Remnant Low Pressure Area because upper-level winds have battered at her.
Despite being downgraded to a remnant low, she's still packing quite a lot of rainfall, and that's what Puerto Rico and the Virgin Islands are getting today, September 4. The National Hurricane Center's final advisory on Erika last night at 11 p.m. EDT noted that her ill-defined center was located 115 miles south-southeast of San Juan, Puerto Rico.
At 8 a.m. today, the remnants of Tropical Depression Erika are located just south of Puerto Rico and are moving slowly westward at 5 to 10 mph. While shower and thunderstorm activity has increased over the past few hours, upper-level winds are not currently favorable for re-development of this system.
Forecasters can't count Erika out yet, so they're giving her a "30 percent chance of regenerating" into a tropical cyclone over the weekend. Although the upper-level winds aren't in her favor, the warm waters of the Caribbean are there, but it takes both to power a tropical cyclone.
The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured Erika's remnant clouds on September 4 at 2:23 a.m. just to the east of Puerto Rico. The remnants don't even resemble the shape of a tropical storm, and appear amorphous on satellite imagery. Infrared imagery measures temperatures and not only can it see cold, high cloud tops in tropical cyclones, but warm ocean waters. The ocean waters in the infrared image are clearly warm enough to support a tropical cyclone (80 degrees Fahrenheit), but the upper level winds have torn Erika apart.
Looking back at her history, Erika formed from a strong tropical wave that moved off of the coast of West Africa and into the Atlantic on August 26. As the wave propagated westward through the central Atlantic, shower and thunderstorm activity associated with the wave increased. The Tropical Rainfall Measuring Mission satellite (known as TRMM) was placed into service in November of 1997. From its low-earth orbit, TRMM has been providing valuable images and information on tropical cyclones around the tropics using a combination of passive microwave and active radar sensors, including the first precipitation radar in space. TRMM is a joint mission between NASA and the Japanese space agency JAXA.
TRMM captured an image of the wave at 04:07 UTC (12:07 am EDT) September 1, 2009 before the system became a named tropical storm. The image showed the horizontal pattern of rain intensity within the storm. Rain rates in the center swath are based on the TRMM Precipitation Radar (PR), and those in the outer swath on the TRMM Microwave Imager (TMI).The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS).
TRMM revealed that there areas of intense rain associated with strong thunderstorm activity at the center of the system. These strong showers and thunderstorms are releasing large amounts of heat, which bodes well for future intensification. However, due to the lack of banding or curvature in the rain features, TRMM also showed that the system is still immature and does not have a well-defined cyclonic circulation. Later in the day, the system was upgraded to a minimal tropical storm with sustained winds reported at 45 knots (~50 mph) by the National Hurricane Center (NHC).
Despite the thunderstorm activity and warm waters, southwesterly wind shear kept Erika from intensifying and the system was still a minimal tropical storm at the time of the next TRMM overpass on the night of September 2. TRMM took that second image of Erika at 03:51 UTC on September 3 (11:51 p.m. EDT September 2) 2009. Once again TRMM showed that Erika did not have a well-defined cyclonic circulation, and had no eye or eyewall and very little evidence of curvature in the rain bands. At that time, Erika's sustained winds were reported at just 35 knots (~40 mph) by NHC.
Erika is expected to continue to track toward Puerto Rico and the Dominican Republic and weaken due to the continuing wind shear.
Rob Gutro, NASA/Goddard Space Flight Center and Steve Lang, SSAI/Goddard Space Flight Center
September 3, 2009
A Disorganized Tropical Storm Erika Drenching the Lesser Antilles
Erika is a poorly organized tropical storm, and NASA satellite imagery has confirmed that for the National Hurricane Center.
Despite poor organization, heavy rainfall and gusty winds are a threat to the Lesser Antilles, and later the Dominican Republic and Haiti. Currently, a Tropical Storm Warning Remains In Effect for Dominica, Guadeloupe, St. Martin, St. Barthelemy, Antigua, Barbuda, Montserrat, St. Kitts, Nevis, Anguilla, St. Maarten, Saba, and St. Eustatius.
Erika is expected to produce total rainfall accumulations of 3 to 5 inches over the central and Northern Lesser Antilles, Puerto Rico, and the U.S. and British Virgin Islands, with isolated maximum amounts of 8 inches possible.
The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured Erika on September 3 at 1:41 a.m. EDT. Erika's clouds appear as a rounded area that cover the Leeward Islands today. The tropical storm force winds were from thunderstorms located mostly to the east of her center. Her center has elongated and her minimum central pressure has risen, both signs of further weakening.
At 8 a.m. EDT today, September 3, Erika's maximum sustained winds are near 40 mph. Her center was located 100 miles east-southeast of St. Croix, near 16.9 north and 63.5 west. Erika is moving north-northwest near 8 mph. Estimated minimum central pressure is now up to 1010 millibars, indicating a weakened storm.
The latest forecast track from the National Hurricane Center takes Erika north of the Dominican Republic and toward the Bahamas late in the weekend.
Rob Gutro, NASA/Goddard Space Flight Center
September 2, 2009
Tropical Storm Warnings Up After Erika Forms
Tropical Storm Warnings have been posted for: Antigua, Barbuda, Montserrat, St. Kitts, Nevis, Anguilla, St. Maarten, Saba, and St. Eustatius. That means that Tropical storm conditions are likely within 24 hours. The Northern Leeward islands can expect 2-4 inches of rain, with isolated areas seeing up to 6 inches over the next couple of days as Erika continues on her track.
NOAA's Geostationary Operational Environmental (GOES) satellite, GOES-12 captured a satellite snapshot of Tropical Storm Erika earlier today, September 2 at 7:45 a.m. EDT. NASA's GOES Project, located at NASA's Goddard Space Flight Center, Greenbelt, Md. created the latest satellite image that showed Erika struggling to maintain her intensity as she brings rain to the Leeward Islands. A westerly wind shear is what has caused her strength to wane. Wind shear means winds at different levels of the atmosphere blowing strong enough to interfere with a storm's circulation.
At 8 a.m. EDT today, Erika was a little weaker than she was yesterday when her sustained winds powered up quickly to 50 mph. Now her maximum sustained winds are near 45 mph, but that will be short-lived as she's again expected to re-strengthen tomorrow. Those tropical storm-force winds extend 120 miles out from the center, although mainly to the northeast of the center. The northeast quadrant of a tropical cyclone is typically where the strongest winds are found.
Appearing somewhat disorganized on this morning's GOES-12 satellite imagery, Erika is approaching the Leeward Islands. She's about 160 miles east-southeast of them, near 16.5 north and 59.5 west. Her minimum central pressure is near 1008 millibars. She's moving near 7 mph in a westward direction, but is expected to shift on a west-northwesterly track and speed up a little over the next day or two. That means that her projected track will carry her near or over the Leeward Islands in the next day or two.
Rob Gutro, NASA/Goddard Space Flight Center
September 1, 2009
A 3-D NASA TRMM Image Shows Good Potential for the Next Atlantic Depression
The Tropical Rainfall Measuring Mission passed over a tropical wave located east of the Leeward Islands this morning, September 1 at 12:07 a.m. EDT, and it showed towering thunderstorms, and good potential for development into a tropical depression. When the data was made into a 3-D image it became more evident that there's a good potential that it could become Tropical Depression number six in the Atlantic Ocean.
At NASA Goddard Space Flight Center in Greenbelt, Md., Hal Pierce of the TRMM team created a 3-D image of the storm to show the towering thunderstorms. The image revealed that the towering thunderstorms in the storm's center are just over 15 kilometers (over 9 miles high) which indicate strong convection and a storm that's powering up.
The National Hurricane Center has given this system a very good chance for developing into the next Atlantic tropical depression.
NASA's Aqua satellite also flew over the area earlier today, and the Atmospheric Infrared Sounder (AIRS) aboard captured an infrared image. The image showed cold high clouds in the low pressure area, confirming the high thunderstorms seen by the TRMM satellite.
The low pressure area is about 260 miles east of the Leeward Islands at 2 p.m. EDT and could be developing a well-defined surface center. At 2 p.m. EDT, the National Hurricane Center said there is a "Greater than 50 percent chance of tropical cyclone formation in this area during the next 48 hours, and interests in the northern Leeward islands, .the U.S. and British Virgin Islands and Puerto Rico should monitor the progress of this system.
Rob Gutro, NASA/Goddard Space Flight Center