Update #2 - Hurricane Joaquin May Be Experiencing Eyewall Replacement in NASA Imagery
The National Hurricane Center indicated on October 2 that powerful Hurricane Joaquin may be experiencing eyewall replacement. The eye was visible on NASA Aqua satellite imagery October 1, but obscured twelve hours later. In addition, NASA's RapidScat instrument helped determine what part of the storm had the strongest winds.
An Inside Look at Joaquin's Strongest Winds
On September 30 at about 7:40 p.m. EDT, the International Space Station passed over Hurricane Joaquin in the Bahamas. The RapidScat instrument which flies aboard ISS measures sustained winds over open ocean and saw the hurricane's strongest sustained winds in the north and northwestern quadrants, stronger than 36 meters per second (80 mph/129.6 kph).
Visible Imagery
The Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA's Aqua satellite captured a visible image of Hurricane Joaquin over Bahamas on Oct. 1 at 17:55 UTC (1:55 p.m. EDT). In the image, the eye was still visible. However, twelve hours later, visible imagery from NOAA's GOES-East satellite showed an eye obscured by clouds which forecasters at NOAA said could indicate that the eyewall of the storm was undergoing a replacement.
Eyewall Replacement
In powerful hurricanes, a new eye begins to develop around the old eye. The new eye gradually decreases in diameter and replaces the old eye. When that happens, the intensity of the hurricane usually decreases. Despite the fact that eyewall replacement can mean a weakening in a powerful hurricane, it can also spread the hurricane force winds out over a larger area.
National Hurricane Center (NHC) Forecaster Brennan noted in the 5 a.m. EDT NHC discussion on October 2,"The eye of Joaquin has not been apparent in recent infrared imagery. The last pass of the Hurricane Hunter aircraft through the center around 04Z [midnight] showed indications of a double wind maximum at flight level, which could indicate that an eyewall replacement cycle is underway. The last report from the aircraft indicated that the central pressure still around 935 millibars. The initial intensity remains 115 knots pending the arrival of the next aircraft before 12Z [8 a.m. EDT]. Some fluctuations in intensity are possible during the next 12 to 24 hours due to eyewall replacement."
Warnings and Watches
On October 2, a Hurricane Warning was in effect for the central Bahamas, northwestern Bahamas including the Abacos, Berry Islands, Eleuthera, Grand Bahama Island, and New Providence, and The Acklins, Crooked Island, and Mayaguana in the southeastern Bahamas. A Hurricane Watch was in effect for Bimini and Andros Island.
In addition, a Tropical Storm Warning was in effect for the remainder of the southeastern Bahamas including the Turks and Caicos Islands, Andros Island, Cuban provinces of Camaguey, Los Tunas, Holguin, and Guantanamo.
Latest Update on Joaquin from the National Hurricane Center
At 8 a.m. EDT (1200 UTC), the center of Hurricane Joaquin was located near latitude 23.4 North, longitude 74.8 West. Joaquin was drifting toward the northwest near 3 mph (6 kph). The NHC expects a faster northward motion to begin later today (Oct. 2), followed by a turn toward the northeast and an increase in forward speed tonight and Saturday. On the forecast track, the core of the strongest winds of Joaquin will continue moving over portions of the central and northwestern Bahamas today. Joaquin will begin to move away from the Bahamas tonight and Saturday.
Maximum sustained winds are near 130 mph (215 kph) with higher gusts. Joaquin is a dangerous category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Some fluctuations in intensity are possible during the next 24 hours. Slow weakening is expected to begin on Saturday.
Hurricane force winds extend outward up to 50 miles (85 km) from the center and tropical storm force winds extend outward up to 205 miles (335 km). The minimum central pressure just reported by an Air Force Reserve Hurricane Hunter aircraft is 937 millibars.
For the latest forecasts, visit the NHC website: www.nhc.noaa.gov.
The NHC noted that gradual weakening is forecast after October 3 as the cyclone encounters increasing southwesterly wind shear, but Joaquin is expected to remain a powerful hurricane for the next several days.
October 02, 2015 - Update #1 - A 3-D Look at Hurricane Joaquin from NASA's GPM Satellite
This 3-D view of Hurricane Joaquin was created using data from The Global Precipitation Measurement (GPM) Dual-frequency Precipitation Radar on September 29th, 2015 at 21:39 UTC (5:39 p.m. EDT). The visualization shows a large area of very intense rain with rain rates ranging from around 50 to 132 mm/hr (~2 to 5 inches) just to the right of the center. This is a strong indication that large amounts of heat are being released into the storm's center, fueling its circulation and providing the means for its intensification.
Associated with the area of intense rain is an area of tall convective towers with tops reaching above 16 km (9.9 miles). The blue snow aloft shows an anvil shape with precipitation gathering to the western part of the storm. This feature indicates that vertical wind shear (difference of winds with height) is strong, and can serve to rip a storm apart.
At the time of this view, the National Hurricane Center reported that Joaquin's maximum sustained winds had increased to 65 mph from 40 mph earlier in the day, making Joaquin a strong tropical storm but poised to become a hurricane, which occurred at 8:00 a.m. EDT.
Image: SSAI/NASA/JAXA, Hal Pierce, Text: SSAI/NASA, Steve Lang
Oct. 01, 2015 - Update #3 - Satellites Show Joaquin Become a Category 4 Hurricane
Hurricane Joaquin had become a Category 4 hurricane on the Saffir-Simpson Wind Scale by 2 p.m. EDT on Oct. 1. At NASA, satellite imagery from NOAA's GOES-East satellite was compiled into an animation that showed the hurricane strengthening. Earlier in the day, NASA-NOAA's Suomi NPP satellite saw powerful thunderstorms within, indicating further strengthening.
The GOES-East satellite is managed by NOAA, and at NASA's GOES Project at the NASA Goddard Space Flight Center in Greenbelt, Maryland, imagery from GOES-East we compiled into an animation. The infrared and visible imagery from Sept. 29 to Oct. 1 from showed Hurricane Joaquin become a major hurricane in the Bahamas.
Earlier in the morning, NASA-NOAA's Suomi NPP satellite passed over Joaquin at 06:10 UTC (2:10 a.m. EDT) as it was strengthening from a Category 2 to a Category 3 hurricane. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard captured an infrared image that showed cloud top temperatures colder than -63F/-53C, indicative of powerful storms within the hurricane. NASA research has shown that storms with cloud tops that high (and that stretch that high into the troposphere) have the capability to generate heavy rain.
On Oct. 1, a Hurricane Warning was in effect for the Central Bahamas, Northwestern Bahamas including the Abacos, Berry Islands, Eleuthera, Grand Bahama Island, and New Providence, The Acklins, Crooked Island, and Mayaguana in the southeastern Bahamas. A Hurricane Watch was in effect for Bimini and Andros Island, and a Tropical Storm Warning was in effect for the remainder of the southeastern Bahamas excluding the Turks and Caicos Islands and Andros Island.
At 2 p.m. EDT (1800 UTC), the center of Hurricane Joaquin was located near latitude 23.0 North, longitude 74.2 West. Joaquin was moving generally southwestward at about 6 mph (9 kph), and the National Hurricane Center forecast a turn toward the northwest and north on Friday, Oct. 2. On the forecast track, the center of Joaquin will move near or over portions of the central Bahamas today and tonight and pass near or over portions of the northwestern Bahamas on Friday, Oct. 2.
Reports from an Air Force Reserve Hurricane Hunter aircraft indicated that maximum sustained winds have increased to near 130 mph (210 kph) with higher gusts. Joaquin is now a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Some additional strengthening is possible during the next 24 hours, with some fluctuations in intensity possible Friday night and Saturday.
Hurricane force winds extend outward up to 45 miles (75 km) from the center and tropical storm force winds extend outward up to 140 miles (220 km).
The latest minimum central pressure extrapolated from Hurricane Hunter aircraft data is 936 millibars. For effects on the Bahamas, updates to forecasts, watches and warnings, visit the National Hurricane Center website: www.nhc.noaa.gov.
The NHC updated forecast takes Joaquin on a more northerly track from Saturday, Oct. 3 through Tuesday, October 6 toward Long Island, New York. Tracks and forecasts are subject to change.
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