VIIRS Day Night Band visible imagery (at 0.7 µm) on 23 October, above, shows a dark patch over the Mid-Atlantic right to the east of New Jersey and the Delmarva peninsula. Chesapeake Bay waters are also much darker than most of the adjacent Atlantic Ocean. Dark patches such as these are associated with light (or no) winds (as noted here and here on this Blog). A lack of winds means the unperturbed sea surface will reflect less moon light back to the satellite. Winds are indeed light around Chesapeake Bay, as shown below. Sparse wind observations over the ocean also suggest light winds in/around the dark patch; this surface analysis shows that the region of the oceanic dark patch is within a ridge of High Pressure where light winds would be expected.

RAP13 model winds (at 10m Fixed Height Above Ground) were also very light in the vicinity of the dark patches of water — with speeds around 3-4 knots over the Atlantic, and 3-4 knots (or less) over the Chesapeake Bay and just east of the Delmarva Peninsula (below).

NOAA-20 VIIRS Day/Night Band image, with an overlay of RAP13 model 10-meter wind vectors (yellow) — and a cursor sample of the wind speed over the Atlantic Ocean (courtesy Scott Bachmeier, CIMSS) [click to enlarge]

NOAA-20 VIIRS Day/Night Band image, with an overlay of RAP13 model 10-meter wind vectors (yellow) — and a cursor sample of the wind speed over the southern Chesapeake Bay (courtesy Scott Bachmeier, CIMSS) [click to enlarge]

Metop-C ASCAT data from early on 23 October, below (from this site), also show very light winds near the dark spots.

The VIIRS ACSPO SST analysis toggled below with the Day Night Band shows that the dark oceanic patch is in a region of relatively cooler water east of the North Wall of the Gulf Stream. That cooler surface could suppress any kind of atmospheric convection that might transport higher velocity down to the ocean surface.

Day Night Band imagery in this post is actually from NOAA-20, not Suomi-NPP. Thanks to Kathy for alerting me to this great case!

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From a Slack Channel (because email is so 2012!) comes a link to RealEarth (imagery shown below) that shows Advanced Clear-Sky Processor for Oceans (ACSPO) estimates of SSTs. The sinuous bendings of the Gulf Stream include a pronounced warm eddy with a ragged thermal edge. (The exercise in determining whether this is inertial instability in this anticyclonic gyre is one that is left to the reader). A zoomed in view of the anticyclone is below. VIIRS has excellent horizontal resolution (375 m) that allows the great imagery shown. A larger view that covers much of the western Atlantic is here.

This derived-from-VIIRS imagery was processed by CSPP software at the CIMSS Direct Broadcast sites, and ingested into an LDM feed for AWIPS. The image below from AWIPS can be sampled to show temperature values. Gulf Stream SSTs leading into the anticyclonic gyre (red-orange in color) are around 79^oF (they are warmer than 80^oF (red/white in the color) at the western edge of the domain, south of New England); the cooler temperatures (south of the gyre; green in the enhancement) are close to 68^oF.

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Tropical Storm Nadine made landfall in Belize on 19 October (at 1600 UTC), and parts of this system then crossed Central America and entered the Pacific Ocean (Here is the NHC discussion that mentions this — from 1500 UTC on 20 October). Tropical Storm Kristy formed off the coast of Mexico later in the day on the 21st of October. The GOES-16 animation of clean window infrared imagery, below, shows the cloud features associated with both systems. Nadine maintained a detectable cyclonic rotation through about 1200 UTC on 20 October. Subsequent to that time, the clouds associated with Nadine moved into central Mexico as a large convective complex developed over the Pacific Ocean to the south of Mexico — this is the system that became Kristy.

It does happen occasionally that tropical systems in the Atlantic traverse Central America and become tropical systems in the Pacific. Although these two systems, Nadine and Kristy, shared the same airmass, they are not the same system.

Scatterometry data (from the manati site) from OSCAT (below) and from ASCAT (at bottom), show the evolution from strong northerly winds over the Gulf of Tehuantepec that quickly coalesce into a strong tropical circulation.

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MIMIC Total Precipitable Water fields for the 24 hours ending 1800 UTC on 21 October 2024, above, show a stream of rich moisture pulled northward into Alaska ahead of a strong storm over western Russia. The result was large snowfall rates over much of central and northern Alaska, as shown in the snowfall rate from this website (here is a Quick Guide on MIRS Snowfall rate) animation below. Two principle bands of snow are indicated, one over eastern Alaska, oriented south-southeast to north-northwest, and one over north-central Alaska, oriented by southeast to northwest.

There are NOAA-20 and NOAA-21 overpasses in the animation above, and data (infrared and microwave) from those satellites can be used to create vertical profiles of temperature, that is, NUCAPS profiles. Those profiles can be gridded to show swaths of thermodynamic variables, such as the 850-mb temperature field shown below. The colorbar has been edited in AWIPS so that values near 0^oC (i.e., the melting point), are black. However, many regions show temperatures at 850 mb colder than 0^oC, but with rain observed at the surface! A possible reason in this discrepancy is that the data being used in the gridding in central AK is from soundings that did not converge, or from soundings that include only microwave data (that is, the infrared retrieval did not converge to a solution). See the image at the bottom, showing ‘Data Quality’; yellow shows profiles for which the infrared retrieval failed (but the microwave retrieval did not) red are regions where both infrared and microwave retrievals failed. It’s also possible that some of these points are below ground! There are many things to consider when interpreting NUCAPS temperature fields.

Just how unusually moist is this airmass over Alaska? Percent of Normal fields, from this site, show values in excess of 200% of normal!

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