NASA-NOAA satellite finds wind shear pushing on Tropical Storm Isaac's center

September 13, 2018

Wind shear seems to be affecting several storms in the Atlantic Ocean today, Sept. 13, 2018. Wind shear is affecting Hurricane Helene in the Eastern Atlantic and in the Western Atlantic, Hurricane Florence and even Tropical Storm Isaac are feeling its effects.

NASA-NOAA's Suomi NPP satellite provided an infrared look at Tropical Storm Isaac that revealed its circulation center was displaced from the bulk of clouds and precipitation. That's an indication that wind shear is affecting the storm.

What is Vertical Wind Shear?

In general, wind shear is a measure of how the speed and direction of winds change with altitude. In order to understand how it affects a tropical cyclone or hurricane, think of a tropical cyclone as a series of vertically stacked tires, all rotating. As you go up from the ground, each tire represents the rotation of the storm's center at a higher level in the atmosphere. The different levels of rotating winds in the center of tropical cyclones need to be stacked on top each other to strengthen. If there are winds higher up that push some of the tires askew near the top, it affects the balance and rotation of the tires below. That's what happens when vertical wind shear pushes against a storm. It pushes the center and weakens (or wobbles) the rotation of all of the tires.

The Satellite Data Reveal

The National Hurricane Center or NHC noted "Satellite imagery indicate that Isaac remains a poorly organized tropical cyclone, with the low-level center mostly exposed during the early morning hours." Isaac is being battered by strong vertical wind shear.

At 1:54 a.m. EDT (0554 UTC) on Sept. 13, the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard NASA-NOAA's Suomi NPP satellite analyzed Tropical Storm Isaac in infrared light. VIIRS found a small area of coldest cloud top temperatures off-center were as cold as or colder than minus 70 degrees Fahrenheit (minus 56.6 degrees Celsius).

NASA research has found that cloud top temperatures as cold as or colder than the 70F/56.6C threshold have the capability to generate heavy rainfall.

At 8 a.m. EDT (1200 UTC) radiosonde data from the eastern Caribbean and NOAA Hurricane Hunter aircraft data indicate that the circulation of Isaac is fairly shallow and small. It is entirely possible that Isaac will degenerate into a tropical wave during the next day or two due to the continued effects of strong wind shear.

Warnings and Watches on Sept. 13

A Tropical Storm Warning is in effect for Martinique, Dominica and Guadeloupe. Tropical Storm Watch is in effect for Antigua, Barbuda, Montserrat, St. Kitts and Nevis, Saba and St. Eustatius, St. Martin and St. Maarten.

Isaac's Stats on September 13, 2018

At 8 a.m. EDT (1200 UTC), the center of Tropical Storm Isaac was located near latitude 15.2 degrees north and longitude 60.9 degrees west. Isaac is moving faster toward the west near 21 mph (33 km/h). This general motion is forecast to continue today with a decrease in forward speed over the Caribbean Sea. Maximum sustained winds remain near 45 mph (75 kph) with higher gusts. Little change in strength is expected over the next several hours as Isaac moves through the Leeward Islands. Gradual weakening is forecast after that as Isaac moves through the eastern Caribbean.

Rainfall Anticipated in Leeward and Windward Islands

NHC said Tropical Storm Isaac is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up to 6 inches across Martinique, Dominica, and Guadeloupe, especially over elevated terrain. Rainfall of 0.5 to 1.5 inches with isolated amounts to 3 inches are forecast across Puerto Rico and the southern United States Virgin Islands, with up to an inch anticipated across the remaining Windward and Leeward Islands. This rainfall may cause dangerous flash flooding.

Isaac's Forecast Path

NHC said on the forecast track, Isaac should move across the central Lesser Antilles and into the eastern Caribbean Sea later today, and then move across the eastern and central Caribbean Sea through the weekend.
-end-
For updated forecasts, visit: http://www.nhc.noaa.gov

NASA/Goddard Space Flight Center

Related Hurricane Articles from Brightsurf:

Hurricane resilience in the Bahamas
A new Stanford-led study provides information on how to invest in natural coastal ecosystems that the Bahamian government, community leaders and development banks are applying in post-disaster recovery and future storm preparation in the Bahamas.

NASA finds a weaker hurricane Juliette
Hurricane Juliette has been weakening and NASA-NOAA's Suomi NPP satellite provided a look at the strength of storms within.

NASA sees Dorian become a hurricane
NASA's Terra satellite passed over the northwestern Atlantic Ocean as Dorian reached hurricane status during the afternoon of August 28, 2019.

Landslides triggered by Hurricane Maria
Hurricane Maria hit the island of Puerto Rico on 20 September 2017 and triggered more than 40,000 landslides in at least three-fourths of Puerto Rico's 78 municipalities.

NASA sees Atlantic's Leslie become a hurricane
NASA's Aqua satellite captured an infrared image of Hurricane Leslie that revealed strong storms circled the center.

NASA sees Walaka becoming a powerful Hurricane
The Global Precipitation Measurement mission or GPM core satellite passed over the Central Pacific Hurricane Center and analyzed Walaka's rainfall and cloud structure as it was strengthening into a hurricane.

NASA finds a weaker Hurricane Olivia
Infrared data from NASA's Terra satellite revealed that the area of coldest cloud topped thunderstorms has dropped from the previous day, indicating weaker uplift and less-strong storms

NASA looks at heavy rainmaker in Hurricane Lane
Cloud top temperatures provide scientists with an understanding of the power of a tropical cyclone.

Hector weakens but remains Category 4 Hurricane
Hurricane Hector has weakened slightly but still remains a robust Category Four storm at present.

UA forecast: Below-average hurricane activity
The UA hurricane forecasting model, which has proved to be extremely accurate over the years, is calling for fewer hurricanes in the Atlantic this year on the heels of a devastating 2017.

Read More: Hurricane News and Hurricane Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.