A comparison of Suomi NPP VIIRS true-color Red-Green-Blue (RGB) images on 07 September (before Irma) and 11 September (after Irma) revealed a marked increase in turbidity of the shallow Continental Shelf waters off the coast of southern/southwestern Florida and the Florida Keys. Irma moved through that region on 10 September as a Category 3 hurricane — and even though the center of Irma moved northward off/along the west coast of Florida (with a wind gust to 75 mph at Key West) , the strongest winds were recorded along/near the east coast of Florida: wind gusts to 92 mph and 109 mph and 142 mph — stirring up particulates within the shallow Continental Shelf waters.

* GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing *

Large-scale (CONUS) VIIRS true-color before-Irma and after-Irma images are available here and here. Note that the cloud shield of Irma had expanded as far westward as Kansas, Texas and Oklahoma on 12 September ( GOES-16 true-color images) — in addition to large areas of dense smoke from wildfires in the Pacific Northwest (blog post) which was drifting eastward across the northern US.

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Suomi NPP overflew Florida and Hurricane Irma shortly after 0700 UTC on Monday 11 September. The 10.8 µm Infrared Image from the VIIRS Instrument, above, shows cold cloud tops and strong convection over much of central Florida (Orlando International Airport received 3″ of rain between 0300 and 0600 UTC on 11 September, as shown in a time series plot of surface data).  The center of Irma at this time was about 55 miles northeast of Tampa.

Suomi NPP includes a Day/Night Band on the VIIRS Instrument, allowing night-time visible imagery that is illuminated by the Moon.  The Day/Night Band Near Constant Contrast product from the same time as the infrared image above, but zoomed out, is shown below. In addition to the cloud structures, this band can help identify power outages. Tampa and Miami city lights are still visible. Key West is dark. A zoomed-in view of Key West (here) shows very little illumination.

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

In addition, GOES-16 “Clean” Infrared Window (10.3 µm) images with surface wind gusts (in knots) are shown below during that night and the following daytime/evening hours on 11 September 2017 — Irma was eventually downgraded to a Tropical Storm and then a Tropical Depression (NHC Discussions) as it moved northward across the Florida peninsula and into southern Georgia and South Carolina.

GOES-16 Water Vapor animations, below, show the evolution of the Hurricane as it transitions to an extratropical cyclone. At the start of the animations, near 0400 UTC on 11 September, the convection in the center of the hurricane is apparent between Tampa and Cape Canaveral. That central convection diminishes with time as it moves northeast and as the extratropical transition continues.

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GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

GOES-16 Infrared Imagery, above, shows Hurricane Irma moving north on a wobbly path (displaying trochoidal motion) through the Florida Keys. The eye of the storm moved between Key West (surface data plot) and Marathon (surface data plot) around sunrise on 10 September. Also note the development of well-defined transverse banding well to the northwest and north of the storm center — a cloud signature often associated with high-altitude turbulence. (In addition, GOES-16 Infrared images during 09-10 September with plots of surface wind gusts in knots is available here). Irma is a storm increasingly affected by wind shear, as evidenced by the asymmetries in the upper level clouds. and as noted in the 1200 UTC 10 September 2017 Wind Shear analysis below (Source).

 

Irma is being influenced by a mid-latitude system and is gradually starting the extended process of extratropical transition. The drying associated with the mid-latitude system is very apparent over the Gulf of Mexico in the animation of 6.95 µm (Mid-level Water Vapor) Infrared Imagery from GOES-16, below.

 

MIMIC TPW, below (source), shows the convergence of residual Atlantic frontal moisture from the east (into northern Florida) and Hurricane Irma’s moisture fro the the Caribbean (into southern Florida) (Click to animate).

Suomi NPP overflew Irma at 0740 UTC on 10 September, and Day/Night Band Visible Imagery (0.70 µm) is toggled with Infrared Imagery (11.45 µm) over the eye, below.

During the subsequent daytime hours, VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1855 UTC, below, showed the eye of Category 3 Hurricane Irma about 40 minutes prior to landfall at Marco Island, Florida.

 

A toggle through 6 different Suomi NPP Channels near the time of landfall (0.41 µm, 0.64 µm, 0.86 µm, 1.38 µm, 1.61 µm and 10.8 µm) is shown below.

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GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

Hurricane Irma hit Cuba as a category 5 Storm late on 8 September 2017. The animation above shows the storm paralleling the north coast of Cuba; outer rainbands are moving into southern Florida. Irma is forecast to turn northwest and north during the day on 9 September, and then move up along the Gulf Coast of Florida, threatening the entire Florida Peninsula with Hurricane-force winds. Irma’s prolonged proximity to the Cuban landmass has affected the storm’s structure and its satellite presentation.  (Compare this animation above to one from 8 September in this blog post). The microwave animation, below, (source) suggests that the disruption to the storm might include the eyewall, and the central pressure of the storm has increased.

 

Wind shear in the atmosphere, shown above as 850-250 mb wind shear (Source), remains very low over the storm.   Shear will increase over the storm during the day however as it moves north.  This could slow any intensification that might occur as the storm moves over the very warm waters of the Florida Straits and eastern Gulf of Mexico, where Sea-Surface Temperatures are 30-32 C.

The latest Geostationary Lightning Mapper data over the storm (from this source) as the sun rises, shows little lightning over the center of Irma.

William Straka, CIMSS, provided the Suomi NPP Visible (from the Day Night Band) and Infrared Imagery below.

A zoomed-in, annotated view of the eye is below. (Click here for an image with no labels)

For further information on this dangerous storm, consult the National Hurricane Center, or the CIMSS Tropical Weather Website.

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