Flooding rains over the Chesapeake Basin

August 12th, 2014
MIMIC Total Precipitable Water for the 72 hours ending at 1800 UTC 12 August 2014 (click to enlarge)

MIMIC Total Precipitable Water for the 72 hours ending at 1800 UTC 12 August 2014 (click to enlarge)

Very heavy rain has fallen during the day on August 12th in and around Baltimore (with rainfall rates as high as 2.70″ per hour at KBWI) and Washington DC, with reports of up to 10″. Where has this moisture come from? There are a variety of products available to diagnose total precipitable water in the atmosphere. The animation above, taken from the MIMIC Total Precipitable Water page (link), shows an influx of tropical moisture from the south-southeast has surged northward up to the east coast of Maryland on August 12. A mesoanalysis from SPC also suggests a link to the moisture east and south of Cape Hatteras. The GOES Sounder Total Precipitable Water derived product image at 1800 UTC, below, (from this website) showed very high total precipitable water amounts just south of Baltimore and Washington DC with values exceeding 60 mm or 2.4″. Soundings at 1200 UTC also showed high values of precipitable water: 48.5 mm or 1.90″ at Wallops Island, VA, and 44.7 mm or 1.76″ at Washington Dulles. Finally, the Blended Total Precipitable Water Product from NESDIS showed values around 51 mm or 2″ as well. (Values did not quite reach the 200% of normal threshold, however).

GOES Sounder Total Precipitable Water derived product image at 18 UTC

GOES Sounder Total Precipitable Water derived product image at 18 UTC

The animation of GOES-13 Infrared (10.7 µm) imagery, below, suggests some training was occurring in the thunderstorm development: thunderstorms continually redeveloped and moved over the same region. Training thunderstorms in moisture-rich air is a recipe for flooding.

GOES-13 10.7 µm infrared imagery on 12 August 2014 (click to animate)

GOES-13 10.7 µm infrared imagery on 12 August 2014 (click to animate)

Comparisons of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:16 UTC and 18:54 UTC (below) showed that the convection exhibited cold cloud-top IR brightness temperatures (as cold as -77º C), and subtle shadowing on the visible imagery suggestive of overshooting tops. Using GOES-13 IR imagery,  the CIMSS/NASA Langley Automated Overshooting Tops / Thermal Couplets product displayed one distinct overshooting top (blue square symbol) over the Baltimore area at 18:45 UTC.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:16 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:16 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:54 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:54 UTC

Iselle approaches the island of Hawai’i

August 7th, 2014
GOES-15 Visible Channel (0.62 µm) imagery (click to play animation)

GOES-15 Visible Channel (0.62 µm) imagery (click to play animation)

GOES-15 visible imagery from after sunrise on 7 August 2014 shows the approach of Pacific Hurricane Iselle towards the ‘Big Island’ of Hawai’i. Orographically-forced clouds are apparent on the northern shores of the entire Island chain, and significant rains are possible as the storm passes — Flash Flood Watches are up for the entire state until 6 AM (HST) Saturday.

There are products available to assess how much rain could potentially fall. For example, the Orographic Rain Index (ORI) uses Total Precipitable Water, 850-mb winds from the Global Forecasting System (GFS) Model and high-resolution topography to determine how much rain might occur if winds are orthogonal (or nearly so) to topography. A real-time display of the product is here.

GOES-15 Water Vapor Channel (6.5 µm) imagery at 1200 UTC 7 August (click to enlarge)

GOES-15 Water Vapor Channel (6.5 µm) imagery at 1200 UTC 7 August (click to enlarge)

The moisture environment surrounding Iselle appears to be less hostile today. The water vapor imagery from 1200 UTC, 6 August, showed significant dry air between the storm and Hawaii. That dry air is not so pronounced today (above). Both images cover the same domain and use the same enhancement. Hurricane Julio is apparent in the eastern part of the image from 7 August, above; that storm is forecast to remain north of the island chain.

GOES-15 Infrared Channel (10.7 µm) imagery (click to play animation)

GOES-15 Infrared Channel (10.7 µm) imagery (click to play animation)

GOES-15 Infrared Channel (10.7 µm) imagery from 7 August shows periodic deep convection forming in the northern half of Iselle’s circulation, north of an eye-like structure in the infrared. The plot of overshooting tops around Iselle (here) shows that overshoots are being detected again after a relatively quiescent period yesterday and the day before.

Morphed Microwave Imagery of Iselle (click to enlarge)

Morphed Microwave Imagery of Iselle (click to enlarge)

Microwave data can be used to measure the intensity of precipitation in/around a tropical cyclone, and the MIMIC-TC pages show animations for active storms. The animation above shows Iselle’s slow weakening — as measured by the intensity of the precipitation in the eyewall.

Mesovortices within the eye of Hurricane Iselle

August 4th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (above; click to play animation; also available as an MP4 movie) revealed the presence of mesovortices within the eye of Category 4 Hurricane Iselle on 04 August 2014. Mesovortices are sometimes seen in the eye and eyewall of tropical cyclones that are going through a period of intensification.

Before sunrise, a 10:30 UTC comparison of GOES-15 10.7 µm IR and TRMM TMI 85 GHz microwave images from the CIMSS Tropical Cyclones site (below) showed that Iselle was beginning to exhibit the appearance of an annular hurricane; note that the ring of high-intensity rainfall within the eyewall was much larger on the microwave image than the “cloud-free” eye that was seen on the IR image.

GOES-15 10.7 µm IR and TMI 85 GHz microwave images

GOES-15 10.7 µm IR and TMI 85 GHz microwave images

========================= Update, 5 August 2014 ==========================

Hourly imagery from 1300 UTC on 4 August to 1300 UTC 5 August shows Iselle maintaining a generally westward track. Cloud-top temperatures have warmed over the 24 hours shown, however, and the eyewall is becoming less distinct. Iselle’s path has been over SSTs that are progressively cooler. Further weakening is expected today.

GOES-15 10.7 µm infrared channel images (click to play animation)

GOES-15 10.7 µm infrared channel images (click to play animation)

Suomi NPP overflew Iselle late in the afternoon of the 4th, and a true color image of the storm is shown below (Image Source: NOAA Hawaii X/L Antenna). A mesovortex can be identified in the eye in this high-resolution image.

Suomi NPP True Color Imagery of Iselle, 2300 UTC 4 August 2014 (click to enlarge)

Suomi NPP True Color Imagery of Iselle, 2300 UTC 4 August 2014 (click to enlarge)

40 years of Satellite Imagery

June 27th, 2014
Synchronous Meteorological Satellite (SMS-1) 11 µm infrared channel image, 2130 UTC 27 June 1974 (click to enlarge)

Synchronous Meteorological Satellite (SMS-1) 11 µm infrared channel image, 2130 UTC 27 June 1974 (click to enlarge)

The oldest satellite image in the SSEC data archive is shown above, taken 40 years ago on 27 June 1974, from SMS-1 (the corresponding visible image can be seen here). The infrared channel sensed radiation in a broad spectrum between 10.5 and 12.6 µm (source). The SMS-1 satellite (launched on 17 May 1974) was positioned over the Equator over eastern South America, at about 45 degrees West Longitude.

More information on the SSEC Datacenter archive is here.