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Hurricane Lorenzo from morning of 28 September 2019

Posted: September 28, 2019

Lorenzo was again observed by three satellites this morning. At 0300Z, the NHC Public advisory reported that Lorenzo had weakened to a Category 3 storm with winds of 120mph and by the 0900Z public advisory, Lorenzo had weakened further with winds of 115mph, just above the threshold for a Category 3 storm. However, the main point is that Lorenzo was weakening during this time period.
Lorenzo was again captured by three different satellites. First by NPP at 0334Z (not shown, since it was on the extreme edge of scan), then NOAA-20 at ~0444Z, then GCOM-W1 at ~0505Z and finally again by NPP at 0534Z.
With the the overlapping scans of N20 and NPP, one could continue to see the temporal changes between scans, as show in the 11μm (I05) slider below:
As can be seen, the 0543Z NPP pass was on the edge of scan which means there are some noticeable parallax effects in the imagery. This parallax effect also extends to the mesospheric gravity waves, which could be seen due to the fact that it was a waning crescent moon (2% illumination).
Something interesting to note is that the mesospheric gravity waves from Lorenzo could be seen up to 1180km (~was 733mi) away.
While this isn’t that unheard of, it is still worth to note. The other obvious thing that can be seen in the IR and DNB imagery is the sort of lopsidedness in the convection (i.e. it isn’t as circular). This is where microwave imagery is useful
AMSR2 was again used in the NHC forecast discussion at 0900Z,  where it was stated:


Lorenzo's tilt has grown this morning. AMSR2 imagery at 0505 UTC showed a 20 n mi displacement between the low- and mid-level centers of the hurricane, a consequence of persistent westerly wind shear. Satellite-based intensity estimates vary greatly, from 77 to 110 kt, so the intensity is set to 100 kt as a compromise of all available data. Despite the decrease in Lorenzo's maximum winds during the past 24 hours, earlier ASCAT-C data showed that its hurricane-force wind field has expanded, and now reaches up to 45 n mi to the northeast of the center.

This tilt could be seen by using the 89Ghz and 26.8Ghz brightness temperatures, shown below

If you look at the images and do a calculation of the distance between where the circulations are located, you come up with just about the same distance as the forecaster (David Zelinsky) came up with. This is one feature that is worth looking into in order to interpret the structure of a storm away from ground based radar. Also worth noting is the channel 16 (88.2Ghz) ATMS imagery from NOAA-20 also showed a similar structure as the 89.0GHz from AMSR2, though there were some slight rotational differences between the two.

Lorenzo has been moving north-northwest with an expected turn to the north today, followed by a turn toward the north-northeast on Sunday along with continued weakening. Currently there are no immediate impacts to the United States, but the remnants could be affecting Britain and Europe by Friday.