Irma was named a Tropical Storm on 30 August in the far eastern tropical Atlantic. Irma strengthened rapidly on 31 August to a Category 3, Major Hurricane. The NHC Day 4-5 forecast cone on 1 September put Irma just east of the Lesser Antilles as a Major Hurricane. With Irma outside of the GOES-16 5-min CONUS sector and no mesoscale sectors yet positioned over the storm, 15-min imagery was the highest temporal resolution available on the 1st. It is also important to remember that given the distance the storm was from GOES-16 nadir, the perceived spatial resolution was degraded as well.
1-min meso sectors from GOES-16 began tracking Irma on the 3rd. By the 4th, Irma continued to track west as a strong, category 3 major hurricane. 1-min satellite imagery from GOES-16 captured the eye of the storm during the morning of the 4th (Fig 2).
By the morning of 5 September, Irma had strengthened to a category 5 major hurricane with 175 mph sustained winds! 1-min imagery continued to be available over the hurricane, providing striking views. The sandwich product, an image combination discussed in previous blog posts, combines visible and IR window imagery into one image. This visualization provides temperature information about the clouds in the storm while maintaining the high spatial resolution (Fig 3).
Tuesday evening, Irma remained a strong category 5 hurricane packing sustained winds to 185 mph with a minimum central pressure of 926 mb. The NHC forecast had Irma near the southern Florida Peninsula on Sunday (Fig 4).
Hurricane Irma passed over Antigua and Barbuda early on September 6, producing a measured wind gust of 155 mph before the anemometer broke. The 5 AM update from NHC kept Irma as a strong category 5 hurricane, with 185 mph sustained winds and a minimum central pressure of 914 mb. The previous day, GOES-16 began collecting 30-sec imagery over Irma by overlaying the two 1-min mesoscale sectors. 30-sec imagery over Irma continued into the 6th (Fig 5).
Two additional storms were named on Tuesday: Katia and Jose. Katia in the Gulf of Mexico is expected to impact Mexico, while Jose is currently forecast to remain in the Atlantic. A zoomed out view of GOES-16 Water Vapor Imagery from Tuesday night to Wednesday morning reveals these three tropical cyclones. Additionally, the upper-level trough over the eastern US is easily identified. This large-scale feature will continue to move east as a ridge builds behind it. Another smaller-scale trough will then move southeast, weakening the ridge, and helping to determine the eventual track of Irma.
By Thursday early evening, Irma remained a strong category 5 major hurricane, packing sustained winds of 175 mph with a minimum central pressure of 922 mb. Today, we take a look at Irma in all 16 GOES-16 ABI spectral bands (Fig 7). As a reminder, the first two bands are in the visible, the next four are near-IR, and final ten are IR. Bands 8, 9, and 10 are the three water vapor bands. Aside from bands 7 (SWIR) and 12 (Ozone), all of the IR bands have almost the same temperature at the top of Irma since those clouds are at the top of the troposphere, above tropospheric moisture and CO2. The hurricane appears warmer in band 7 due to reflectance of solar radiation off of the cloud tops and Band 12 is warmer due to emission from ozone in the stratosphere where there is a temperature inversion.
The two-day IR loop below shows the category 5 hurricane maintaining strength as it advances toward the US. Use the feature-following zoom tool in AWIPS to create animations such as the one below (Fig 8).
On Friday the 8th, Irma remained a category 4 major hurricane packing 155 mph winds and a minimum central pressure of 924 mb. Irma was expected to turn more north late Saturday and head for the Florida Keys hitting the Keys early Sunday. A seamless transition of GOES-16 imagery from VIS (day) to IR (night) can be accomplished in AWIPS (Fig 9). Simply overlay VIS on IR, and make the lowest portion of the VIS color-table (0 – 0.5) transparent.
The interaction of Irma with Cuba Friday night into Saturday morning caused it to weaken slightly to a category 3 hurricane with 125 mph max sustained winds and a minimum central pressure of 941 mb at the 11 AM Saturday update. Today we compare visible (Fig 10) imagery from GOES-16 (at 89.5 W) with that from GOES-13 (at 75 W, GOES-East). From GOES-16 today, one mesoscale sector is available over Irma providing imagery every minute. Meanwhile, GOES-13 is operating in Rapid Scan Mode, which provides imagery every 5, 7, 8, and 10 minutes (and 30-minutes every 3 hours for full disk). Spatially, the visible (IR) imagery from GOES-16 is 0.5 km (2 km), while that from GOES-13 is 1 km (4 km).
Early Friday evening, Irma maintained category 3 strength as continued its west-northwest trajectory. Showers, thunderstorms, and strong winds were beginning to impact Florida and the Florida Keys. GOES-16 1-min VIS/IR sandwich combo imagery shows the impressive structure of Irma and thunderstorm activity over Florida.
A few hours later, Irma began the turn north towards the Florida Keys as depicted in GOES-16 IR (Fig 11). Also included in the animation are NLDN cloud-to-ground lightning. There has been quite a bit of lightning activity, as expected, with the outer convective bands in the front right quadrant moving into southeast Florida. Several tornado warnings have been issued with at least two confirmed tornadoes in south Florida.
Hurricane Irma made landfall over the Florida Keys Sunday morning as a category 4 major hurricane. A 20 hour loop ending at 1415 UTC this morning, or just after landfall, shows the sharp turn north Irma took last night and its acceleration to and over the Keys (Fig 12).
Irma again made landfall at 3:35 PM at Marco Island, Florida where a 130 mph wind gust was reported. Irma then advanced to Naples. 30-sec imagery was available from GOES-16 over the hurricane during landfall by overlapping the two mesoscale sectors. In the 30-sec VIS/IR sandwich combo, the eye is apparent along with bubbling convection in the front right quadrant.
-Bill Line, NWS
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