An email from SSEC/CIMSS employee Shane Hubbard discussed details of a weak tornado in San Juan, Puerto Rico on 06 October 2017:

While I was working in San Juan last week a tornado formed close to the shoreline of Lake (Lagoon) Los Corozos, moved over the water, and then damaged homes in a neighborhood named ‘Playita’ where I was working. The tornado formed near 18.439089, -66.041962 on October 6th around 4:25pm AST. 10+ roofs were damaged from the event. Many of those roofs had already been repaired by residents or by the carpenters that were volunteering in the community. It was a very depressing event to say the least.

Here are links to the tornado.

https://www.youtube.com/watch?v=Oc8j4uLPQvg

Approximate tornado path (courtesy of Shane Hubbard)

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

A GOES-16 Mesoscale Sector remained positioned over Puerto Rico (to support their lack of weather radars, which were destroyed by Hurricane Maria; click here for a Tweet from NWS San Juan showing their radar damage) — “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed the region around San Juan (station identifier TJSJ).  An Infrared animation covering the time from 1915 UTC to 2054 UTC, displayed at the GOES-16 ABI full 12-bit depth (created using SIFT) is shown here; a visible animation is available here.

Convective initiation occurred over the far eastern end of the island about an hour before the tornado — cloud-top infrared brightness temperatures cooled to around -70ºC (black enhancement) around the time of the tornado (2025 UTC) during a second burst of convection.

Of particular note is the speed with which the second convective storm grew.  Between 2020 UTC and 2025 UTC, the cloud-top infrared brightness temperatures cooled 20ºC in the region of thunderstorm development!  The bar graphs below show the brightness temperature distribution in the region of convective development.

The animation below shows GOES-16 10.3 µm Clean Infrared Window images for 10 minutes: 2017-2026 UTC on 6 October. Very strong convective development is apparent, overlapping with the 2025 UTC time of the tornado.

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GOES-16 Visible Imagery, above, shows convection (imagery at 1-minute intervals) surrounding Tropical Storm Nate, just onshore in northeastern Nicaragua.

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

The Tropical Depression (#16) in the western Caribbean Sea has strengthened to become a minimal Tropical Storm, acquiring the name Nate. The animation from GOES-16, above, shows disorganized convection over the entire basin, stretching into the Pacific Ocean south of central America. (The sheared remains of Pacific Tropical Storm Ramon are also present south of Mexico). The animation below, from 0000-1300 UTC on 5 October 2017, shows the mid-level Water Vapor Infrared Imagery (6.95 µm) from GOES-16. Convection develops over the center of Nate, over Nicaragua, at the end of the animation.

Microwave Imagery, below, from SSMI/S at around 1000 UTC on 5 October, (from this site) suggests that Nate is centered very near the coast of Nicaragua. Nate is forecast to move north into the Gulf of Mexico; its path through the northwest Caribbean suggests strengthening is possible if Nate remains far enough from land. Very warm water is present in the northwest Caribbean; that warmth extends to great depth as shown by this plot of Oceanic Heat Content; that warmth extends into the central Gulf of Mexico.

Nate formed at a time when the Moon was Full. Thus, Suomi NPP Day Night Band Visible Imagery showed excellent illumination. The image below is from 0627 UTC on 5 October.

Total Precipitable Water in advance of Nate is plentiful, as shown in the loop below (from this site). There is dry air over the continental United States, however, associated with a strong High Pressure System. Easterly winds south of that system are apparent in Scatterometer winds from early in the morning on 5 October.

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The YouTube link, above, shows the GOES-16 “Clean Window” (10.3 µm) Infrared Imagery over the Atlantic, showing the evolution of Hurricanes Franklin through Maria, from 7 August through 1 October. (The original mp4 video (250 Meg) is available.)

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

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

The Accumulated Cyclone Energy (ACE) for September 2017 set a new record for any month over the North Atlantic basin:

Since it was released on a Sunday morning, many missed the monthly summary from NHC confirming Sept 2017 as the most active month on record pic.twitter.com/7T3svWUmQ4

— Eric Blake ? (@EricBlake12) October 2, 2017

Two significant contributors to this record ACE value were long-lived and very intense Hurricane Irma and Hurricane Maria.

Hurricane Irma – Ace: 66.6 – Duration: 13 Days

One noteworthy statistic of Hurricane Irma: during its 3 days and 3 hours as a Category 5 hurricane (above), the storm had an intensity of 160 knots or 185 mph for 37 consecutive hours — which set a new world record. GOES-16 “Clean” Infrared Window (10.3 µm) images during this period of 185 mph intensity (below) showed a well-defined eye, with cold cloud-top infrared infrared brightness temperatures (occasionally -80ºC or colder, denoted by the violet color enhancement) within the adjacent eyewall region.

Hurricane Maria – Ace: 44.6 – Duration: 14 Days

One noteworthy aspect of Hurricane Maria was its intensification to a Category 5 storm on 18 September (above) — just before making landfall on the island of Dominica — and less than 48 hours before making landfall over southeastern Puerto Rico as a high-end Category 4 storm. GOES-16 Infrared Window (10.3 µm) images at 1-minute (pre-landfall) and 30-second (post-landfall) time intervals (below) showed that while the eye of Maria quickly eroded as the tropical cyclone moved northwestward across the island and interacted with its rugged terrain, deep convection of the eyewall region persisted over much of Puerto Rico during the transect. Note that the last hourly surface observations from Roosevelt Roads (TJNR) and San Juan (TJSJ) were from 04 UTC and 09 UTC, respectively — after which times power and communications to weather equipment (such as the San Juan radar) were lost.

Hurricane Jose – Ace: 42.2 – Duration: 17 Days

Although not as intense as Irma or Maria, the long duration of Hurricane Jose allowed it to achieve an ACE value nearly as high.

Individual storm montage images are available here on the CIMSS Tropical Cyclones site.

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