A strong storm is bringing high winds and rain to the east coast of the United States from North Carolina northward to New Jersey. This dangerous weather will persist through tomorrow. The weather results from the combination of the extratropically transitioned remnants of Ida — over southern North Carolina — and a strong high pressure system over New England. (See a surface analysis here). Various satellite-derived products can be used to explore this system.

Consider the water vapor loop above. Towards the end of the loop, features in the vapor are developing and moving westward over Virginia and North Carolina. That observation combined with the continued eastward motion in the water vapor signal over the southeast part of the US suggests the formation of a closed circulation. Such a development will slow the eastward progression of the system, prolonging the period of stormy weather on the coast.

Satellite observations of total precipitable water (a blended product from AMSU and SSM/I on the NOAA series of Polar Orbiters) show large values — greater than 200% of normal — over the eastern United States. Superimposed near-surface winds from the QuikScat scatterometer show a broad region of gale-force winds over the Ocean. The long fetch of the wind over open ocean will allow large waves to develop. (A zoomed-in version of the QuikScat winds, here, includes a 57-knot wind with a rain flag of only 1% — meaning it’s a “good” wind. Peak surface wind gusts from reporting stations on land at this time included 44 knots at Norfolk, Virginia, 43 knots at Wallops Island, Virginia, and 42 knots at Elizabeth City, NC). The long duration of the storm event and the winds will exacerbate matters. A loop of precipitable water derived from SSMI and AMSRE (here) shows the tropical origins of the moisture over the eastern part of the United States, and also the movement of more moisture in from the east.

Abundant moisture is leading to large rainfalls. Rainfall rates are estimated using data from the AMSU instrument on the NOAA series of POES spacecraft. There are numerous pixels in the short loop above, including suggesting rains exceeding 20 mm per hour. There is also a westward drift suggested in the loop.

Visible image loops (rocking loops) from GOES-12 and GOES-14 show the westward drift of clouds into western Virginia and the Carolinas as the system starts to close off. A near-surface circulation center can also be inferred over southern North Carolina.

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MODIS true color images (30 September, 01 November, 10 November)

A sequence of three MODIS true color images from the SSEC MODIS Today site (above) showed an increasing level of turbidity of the water along the Gulf Coast — the 3 images are from 30 September, 01 November, and 10 November 2009. This increase in turbidity can be directly attributed to the runoff of sediment-rich water due to heavy precipitation across much of the Gulf Coast states from late October into early November, as shown in the 14-day observed precipitation map (below). Special thanks to Steve Davis and Jeff Craven at the National Weather Service forecast office at Milwaukee/Sullivan for creating/capturing these images and bringing this case to our attention!

14-day observed precipitation

AWIPS images of the MODIS Sea Surface Temperature (SST) product (below) showed that the Gulf of Mexico immediately offshore was significantly colder due to this discharge of sediment-rich water from rivers draining from the Gulf Coast states — SST values were in the low to mid 60s F (darker green colors) right along the coast, compared to the mid 70s to near 80º F (darker red colors) farther offshore.

MODIS Sea Surface Temperature product (November 10 - 12)

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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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