A morphed microwave imagery loop (from the MIMIC website at CIMSS) shows 48 hours of structural changes as observed from microwave imagery. Note the strong eyewall-like structures at the beginning of the loop, with persistent strong convection noted west of the storm center. As the storm moves over colder water, and as southwesterly shear increases, the structure deteriorates and strong convection becomes concentrated in regions some distance east and north of the storm center.

The color-enhanced loop, above, of 11-micron brightness temperature also shows Hurricane Ida (dowgraded to a Tropical Storm at 9 AM EDT on Monday) moving northward from the Straits of Yucatan into the central Gulf of Mexico. As it moves, the appearance of the storm deteriorates markedly. At the start of the loop, a relatively warm region in the center of the central dense overcast (CDO) that might be the eye of the storm migrates to the southwest edge of the CDO and then vanishes. This change shows the effects of strong southwesterly winds that are moving the tops of the thunderstorm away from the center of the storm.

Maps of shear (wind vector differences between the upper and lower troposphere) show a more hostile environment for the storm between 1200 UTC Sunday — when Ida was a strengthening category 1 hurricane in the Straits of Yucatan — and 1200 UTC Monday, when Ida was a weakening category 1 hurricane over the central Gulf of Mexico. Maps of mid-level shear, that is changes in wind between the lower and middle troposphere, for 1200 UTC Sunday and Monday tell a similar tale.

Ida’s path is forecast over progressively cooler sea-surface temperatures. That in combination with the hostile shear environment suggest that re-strengthening to hurricane status is unlikely. Strong high pressure off the East Coast of the United States, however, as shown in an analysis here suggest a large pressure gradient that will support strong winds over the entire southeast part of the United States as Ida approaches the central Gulf Coast.

Visible imagery, above (from GOES-14), show the results of shear on the cloud patterns. Deep convection is offset to the northeast of the circulation center (shown as the yellow dot in the imagery, from the 1500 UTC National Hurricane Center discussion). Latent heat in the storms cannot affect the southern/western semicircles of the storm if the storms are all displaced by shear to the north and east, as in this rocking loop. A similar loop from GOES-12 is shown here.

Precipitable water estimates from microwave imagery, above, show deep tropical moisture over the Gulf of Mexico. As this tropical moisture moves over the cooler air at the surface over the southeast part of the United States, it will cool and water will condense out. Heavy rains are predicted in the next two days as that happens.

For more information on Ida, please visit the CIMSS Tropical Weather Website or the National Hurricane Center website.

Added: Late afternoon infrared satellite imagery from GOES 14 and visible imagery from GOES 14 show convection nearly wrapping around the center of the storm, just south of the mouth of the Mississippi River. However, persistent shear appears to be over-riding that tendency.

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Tropical Storm Ida has formed in the southwestern Caribbean Sea. Strong convection near the center is evident in the visible image, above, as well as suggestion of a banded feature northeast of the center. The southwestern Caribbean Sea is a region where tropical cyclogenesis can still occur at this time of year because of the combination of two things: (1) still-warm ocean waters (see an analysis of sea surface temperatures from CIMSS here; and (2) small values of vertical wind shear, as shown here. Microwave estimates of Precipitable water (using MIMIC) show that Ida formed in a region of enhanced precipitable water.

Ida is forecast to take a path over Nicaragua and Honduras (the path is depicted in the image of SSTs above (and here) before re-emerging over the still-warm waters of the far western Caribbean.

Update, 5 November. Visible imagery from the morning of 5 November, above, show upgraded Hurricane Ida on the coast of Nicaragua. The visible image shows banded structures over the Caribbean that speak to the increased organization to the system. However, its motion over the rugged terrain of Central America should cause weakening. Torrential rains over the mountains of Nicaragua and Honduras will accompany the storm.

Loops (Visible and Infrared) taken from the CIMSS tropical webpage show the evolution of Ida after landfall. Ida quickly lost intensity to depression status late on the 6th. The storm is forecast to be over the northwest Caribbean, where waters are very warm, over the weekend, so re-intensification is possible.

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The long nights of November allow ample cooling in clear airmasses, and fog is a frequent occurrence over rivers that are still relatively warm compared to the surrounding land. In these near-water locations, cooling to the dewpoint, and resultant saturation, allows fog to form in and along River valleys as shown in the above visible image from GOES-12. The Ohio River and its many tributaries in Pennsylvania, West Virginia and Kentucky are plainly visible.

Detection of fog at night occurs by comparing observed brightness temperatures at about 11 microns and about 3.9 microns. Small water droplets in fog are not effective emitters of radiation at 3.7 or 3.9 microns — that is, they do not emit like blackbodies — but the water droplets are effective emitters of radiation at 11 microns. Thus, the temperature inferred by the satellite (that assumes all bodies are emitting like blackbodies) is cooler for the 3.9-channel than for the 11-micron channel. A difference between the two temperatures, then, can be used to highlight fog.

The MODIS Fog product image, above, from AWIPS, shows the channel difference at 0736 UTC on 2 November, and it suggests ongoing fog in river valleys from New York State southwestward to Kentucky. The nearly simultaneous GOES image (from 0730 UTC) is below. The degraded resolution of the GOES infrared sensor over the Ohio Valley (about 5-km pixels, vs. 1-km pixels for MODIS) means that developing fog, by its nature at very small horizontal scales, is not initially detected. The finer-resolution detector on the MODIS instrument provides earlier warning of developing fog.

Fog in the river valleys is more obvious in the GOES Fog Product image from 1030 UTC, three hours later. However, the pixel footprint of GOES IR sensor means a less defined horizontal mapping of the true fog locations. The higher resolution MODIS instrument gives earlier detection and better horizontal delineation of fog events.

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The Halloween Blizzard of 1991 was an early-season storm that moved north from the Gulf of Mexico to the upper Great Lakes. Unseasonably cold air allowed the rich moisture-laden airmass to deposit a long band of snow from the Panhandle of Texas northeastward to western Lake Superior. Many early-season snow total records were broken, and single-storm records fell at Minneapolis (28.4″) and Duluth (36.9″) Typically storms from the Gulf of Mexico do not move due north; however, eastward motion of this system was blocked by a large nor’easter off the coast of New England (the so-called “Perfect Storm”).

In the visible loop above, notice the rapid melting of snow deposited by the system in the Texas Panhandle, despite record cold (30 and 31 October 1991 are the only October days in Amarillo history when the surface temperature stayed below 30 F all day). Snowcover in South Dakota (the Missouri River stands out) also speaks to the chill in the airmass on the cold side of the storm. A larger-scale visible animation is available here.

Update

The 1991 “Halloween” storm is the “single storm record for the metropolitan (Twin Cities)” area. A comparison of a GOES-7 Infrared and visible image on November 1, 1991 at 21 UTC.

H/T

These NOAA GOES-7 data was accessed via the University of Wisconsin-Madison SSEC Data Services, using the McIDAS-X software.

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