Dry air within an Atlantic subtropical ridge

November 16th, 2018 |

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed a large region of very dry air within a subtropical ridge over the central North Atlantic Ocean on 16 November 2018. Infrared brightness temperatures were unusually warm (brighter yellow to red enhancement) on all 3 Water Vapor bands, especially along the western edge of the dry air.

A GOES-16 Upper-level Water Vapor image at 1700 UTC (below) showed a swath of NUCAPS sounding availability close to that time. The swath passed directly over the driest air within the subtropical ridge.

GOES-16 Upper-level (6.2 µm) Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

GOES-16 Upper-level Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

One of the green (high-quality) NUCAPS soundings within the arc of driest air (below) revealed a remarkably dry profile above the trade wind inversion — dewpoint values were -50ºC and colder within the 500-620 hPa layer, and dewpoint depressions were about 50ºC near the 550 hPa level.

NUCAPS sounding profile within the driest air [click to enlarge]

NUCAPS sounding profile within the driest air [click to enlarge]

Even though the middle to upper tropozphere was quite dry, note that the Total Precipitale Water (TPW) value calculated from the NUCAPS profile was 0.73 inch — there was still abundant tropical moisture within the marine boundary layer of the warm central Atlantic. The GOES-16 TPW product (below) showed minimum values of 0.6-0.8 inch in the region of driest air on the Water Vapor imagery (1800 UTC comparison). In contrast, TPW values over a large portion of the Lower 48 states were 0.6 inch or less, even in regions that appeared to be “moist” on the Water Vapor imagery.

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

Atmospheric River brings precipitation to south-central Alaska

November 12th, 2018 |

Blended Total Precipitable Water product [click to play animation | MP4]

Blended Total Precipitable Water product, with Upper Air sites plotted in white [click to play animation | MP4]

The NESDIS Blended Total Precipitable Water (TPW) product (above) showed an atmospheric river that was transporting moisture northward from the tropics to south-central Alaska during 11 November – 12 November 2018. TPW values were in excess of 2.0 inches near the leading edge of the moisture plume early in the period.

The corresponding Percent of Normal Blended Total Precipitable Water product (below) indicated that these values of TPW were at or above 200 percent of normal (yellow).

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Using the MIMIC Multi-layer TPW site, you can see how TPW is partitioned within various layers of the atmosphere (below). This TPW product uses microwave data from POES, Metop NOAA-20 and Suomi NPP satellites (description). It’s important to keep in mind that the location and continuity of a plume of TPW (such as an atmospheric river) might not always exactly agree what is seen on geostationary satellite Water Vapor imagery, since water vapor spectral bands usually sense radiation being emitted from levels above where the bulk of TPW is normally found (as discussed here).

MIMIC Multi-layer Total Precipitable Water product [click to play animation | MP4]

MIMIC Multi-layer Total Precipitable Water product on 12 November [click to play animation | MP4]

Anchorage, Alaska rawinsonde data (below) showed that TPW values reached a maximum of 0.73 inch at 00 UTC on 12 September.

Sequence of Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

The arrival of this moisture produced heavy rainfall and mixed winter precipitation across the region — Portage Glacier (about 50 miles southeast of Anchorage) received 9.99 inches of rainfall in 48 hours, and Anchorage set a new daily precipitation record on 11 November with 0.89″ (which included 1.0 inch of new snow). A summary of temperature and precipitation reports can be seen here.

A comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November (below) revealed widespread layered clouds across most of south-central Alaska.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]

Super Typhoon Yutu re-intensifies to Category 5

October 26th, 2018 |

Himawari-8

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play MP4 animation]

After making landfall in the Northern Mariana Islands on 24 October, Super Typhoon Yutu underwent eyewall replacement cycles that brought about a drop to Category 4 intensity on 25 October. However, during the day on 26 October 2018 the storm again re-intensified to Category 5 (ADT | SATCON). Himawari-8 “Clean” Infrared Window (10.4 µm) images (above) showed a fascinating variety of storm-top features: (1) outward-propagating gravity waves, (2) a quasi-stationary (in a storm-relative sense, with respect to the moving storm center) curved “notch”  — resembling a hydraulic jump — within the eastern semicircle, and (3) periodic bursts of warm/cold couplets (black/violet enhancement)  — resembling “hot tower” impulses — located well northeast of the storm center (forming around 19-20º N/137º  W) that propagated quickly northwestward. In addition, cloud-top infrared brightness temperatures of -90ºC and colder (yellow pixels embedded within darker purple shades) were seen southern eyewall during the 18-19 UTC period (1834 UTC image).

A comparison of Himawari-8 “Red” Visible (0.64 µm) and Infrared Window images during the few hours after sunrise (below) showed an eye that was partially cloud-filled with low-level mesovortices.

Himawari-8 "Red" Visible (0.64 µm, left) and "Clean" Infrared Window (10.4 µm, right) images [click to play MP4 animation]

Himawari-8 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.4 µm, right) images [click to play MP4 animation]

An animation of Himawari-8 Visible images from 2302 UTC on 26 October to 0632 UTC on 27 October (below) provides a more detailed view of the mesovortices and some of the storm-top gravity waves. As was seen on Infrared imagery, a train of quasi-stationary concentric waves formed along the “notch” feature, becoming especially pronounced around 0532 UTC.

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play MP4 animation]

A comparison of DMSP-17 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images from the CIMSS Tropical Cyclones site (below) showed Yutu around 2130 UTC.

DMSP-17 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images [click to enlarge]

DMSP-17 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images [click to enlarge]

Tropical Storm Michael

October 7th, 2018 |

GOES-16 "Clean" Infrared Window (10.3 µm) images [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images (above) showed deep convection associated with Tropical Depression 14 east of Belize and the Yucatan Peninsula of Mexico early in the day on 07 October 2018. There was a large area of cloud-top infrared brightness temperatures in the -80ºC to -89ºC range (shades of purple), with isolated small pockets of -90ºC or colder (yellow enhancement).

1-minute GOES-16 “Red” Visible (0.64 µm) images from the UW-AOS site (below) showed numerous convective overshooting tops.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

At 1655 UTC the system was upgraded to Tropical Storm Michael — 1-minute GOES-16 Infrared images (below) showed that deep convection persisted in the eastern semicircle of Michael during the remainder of the day.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

A hint of the elongated low-level circulation could be seen just west of the deep convection on late-day GOES-16 Visible images (below).

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

===== 08 October Update =====

NOAA-20 VIIRS Day/Night Band (0.7 µm), Infrared Window (11.45 µm) and ATMS Microwave (88 GHz) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm), Infrared Window (11.45 µm) and ATMS Microwave (88 GHz) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm), Infrared Window (11.45 µm) and ATMS Microwave (88 GHz) images at 0721 UTC (above; courtesy of William Straka, CIMSS) indicated that a well-defined convective band was wrapping around the eastern, northern and northwestern portions of the storm center (with some bright lightning streaks showing up on the DNB image in the southeastern segment of this convective band).

In a comparison of DMSP-18 SSMIS Microwave (86 GHz) and GOES-16 Infrared Window (10.3 µm) images at or shortly after 1115 UTC (below), the Microwave imagery showed a very large eye beneath the convective clusters.

DMSP-18 SSMIS Microwave (86 GHz) and GOES-16 Infrared Window (10.3 µm) images [click to enlarge]

DMSP-18 SSMIS Microwave (86 GHz) and GOES-16 Infrared Window (10.3 µm) images [click to enlarge]

Michael was upgraded to a Category 1 hurricane at 15 UTC; 1-minute GOES-16 “Red” Visible (0.64 µm) images (below) revealed abundant deep convection around the core of the storm during the 3 hours leading up to that time.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

Michael had been moving over very warm water since forming on 06 October; analyses of Ocean Heat Content and Sea Surface Temperature (below) showed that while the hurricane was forecast to briefly pass over a region of lower OHC in the far southeastern Gulf of Mexico, the remainder of its journey across the Gulf would be over water possessing modest amounts of OHC and warm SST values of 29-30ºC.

Ocean Heat Content and Sea Surface Temperature analyses, with past and forecast tracks of Michael [click to enlarge]

Ocean Heat Content and Sea Surface Temperature analyses, with past and forecast tracks of Michael [click to enlarge]

Similarly, a relatively cloud-free Terra MODIS Sea Surface Temperature product from 0343 UTC on 06 October (below) showed SST values of 84-85ºF (darker red colors) along much of the forecast path of Hurricane Michael (issued at 2100 UTC on 08 October).

Terra MODIS Sea Surface Temperature product (0343 UTC on 06 October) with Hurricane Michael forecast positions issued at 2100 UTC on 08 October [click to enlarge]

Terra MODIS Sea Surface Temperature product (0343 UTC on 06 October) with forecast positions of Hurricane Michael issued at 2100 UTC on 08 October [click to enlarge]