ACSPO SSTs off the Oregon Coast

September 14th, 2021 |
ACSPO SST values derived from VIIRS data, 12-14 September 2021, at times indicated (Click to enlarge)

Clear skies to the west of Oregon and California in the past two days have allowed VIIRS data (VIIRS — the Visible-Infrared Imaging Radiometer Suite flying on both Suomi-NPP and NOAA-20) to produce compelling imagery of the Sea Surface using Advanced Clear Sky Processing for Ocean (ACSPO) algorithms. VIIRS imagery is downlinked at the Direct Broadcast site at the UW-Madison; data are processed using CSPP. Purple values are just a bit cooler than 50º F; Yellow values are in the mid-60s ºF.

ACSPO estimates of SSTs are important over the Pacific Northwest because the Level 2 SST GOES-16 product is not computed near the GOES-16 limb. Level 2 Clear Sky mask is not computed out to the limb, as shown below, and GOES-16 SSTs (Full-Disk only products) are not computed out to the edge of the Clear Sky mask! So, if you want satellite-derived SSTs (GOES-17 Level 2 products are not yet widely available), Polar-Orbiting data are the way to go.

GOES-16 Level Clear Sky Mask (white=clouds; black=no clouds) and derived SSTs, 1600 UTC on 14 September 2021 (Click to enlarge)

AWIPS-ready ACSPO SST files are available from via an LDM feed from CIMSS.

Hurricane Nicholas makes landfall in Texas

September 14th, 2021 |
GOES-16 Mesoscale Sector infrared imagery (Band 13, 10.3), 0321-0844 UTC on 14 September 2021

Hurricane Nicholas made landfall on the Gulf Coast shortly after 0530 UTC on 14 September. It is a challenge to determine the storm center from the animation above, although deep convection is suggestive of its location. Note the collapse of deep convection as well at the end of the animation. Radar imagery, below (from this site), is helpful in placing the storm center.

NEXRAD Composite Reflectivity, 0524, 0534, 0544, 0554 UTC on 14 September 2021 (Click to enlarge)

MetOp-B overflew Nicholas at 0315 UTC shortly before landfall. ASCAT winds (from this site) at 0315 UTC show the circulation center very close to the shoreline. A similar image from the OSI SAF Multiplatform viewer is here.

Metop-B ASCAT winds, 0314 UTC on 14 September 2021 (Click to enlarge)

Nicholas is embedded in very moist air. A 24-hour MIMIC Total Precipitable Water animation, below, shows the moisture plume. Heavy rain is forecast for the central Gulf Coast.

Total Precipitable Water, 1000 UTC on 13 September – 0900 UTC 14 September (click to enlarge)

Nicholas has weakened to a Tropical Storm as of 0900 UTC on 14 September. Refer to the National Hurricane Center website for more information.

The beginning of the extratropical transition of Hurricane Larry

September 10th, 2021 |
GOES-16 Airmass RGB, 0000 UTC on 8 September through 1200 UTC on 10 September 2021 (Click to enlarge)

The animation above (created using Geo2Grid) with a 3-h time step shows the approach of a mid-latitute shortwave trough (that produced large hail over Wisconsin on Tuesday 7 September; SPC Storm Reports) to Hurricane Larry over the tropical Atlantic. The Potential Vorticity anomaly associated with the mid-latitude trough (moving from the western Great Lakes on the 8th to the east coast on the 10th) appears as red/orange in the RGB imagery, and by 1200 UTC on the 10th, the anomaly sits over the eastern United States with Larry to its east. The RGB at 1200 UTC on the 10th shows orange/red hues to the south and east of the the hurricane center; in that region, however, the orange colors do not signify upper level potential vorticity anomalies, but rather dry air in the mid-tropopshere.

The correlation between red/orange values in the RGB and large values of potential vorticity in the upper troposphere with the feature in the midwest United States is confirmed by the overlay below that shows a pressure analysis on the 1.5 Potential Vorticity Unit (PVU) surface. The UKMET Office model data shows pressure values below 500 mb.

GOES-16 Airmass RGB (2100 UTC 9 September, 1200 UTC 12 September) and UKMET Model Simulation of 1.5 PVU Pressure values (0000 and 1200 UTC on 10 September), Click to enlarge

NUCAPS (NOAA-Unique Combined Atmospheric Processing System) profiles yield information about the thermal structure of the atmosphere, and also measure ozone concentration. Gridded values from the profiles, shown below (from this url) show a low tropopause and enhanced ozone (both suggestive of a tropopause fold/stratospheric intrusion) over the eastern US at 0647 UTC on 10 September (and also at 1812 UTC on 10 September).

NOAA-20 gridded NUCAPS estimates of Tropopause Height, and of Ozone anomalies, 0647 UTC, 10 September 2021 (Click to enlarge)

For more information on Larry, refer to the webpages of the National Hurricane Center.

Mesovortices within the eye of Hurricane Larry

September 6th, 2021 |

GOES-16 “Clean” Infrared Window (10.35 µm) and “Red” Visible (0.64 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above)  revealed the presence of mesovortices within the eye of Category 3 Hurricane Larry in the central Atlantic Ocean on 06 September 2021.