Tropical Storm Chris

July 8th, 2018 |

GOES-16 Visible Imagery (Band 2, 0.64 µm), from 1837 – 2332 UTC on 8 July 2018 (Click to animate)

Tropical Depression Number 3 was upgraded to Tropical Storm Chris at 0900 UTC 8 July. Chris has been mostly stationary on 8 July. The visible animation, above, from Sunday 8 July shows excellent upper-level outflow to the northeast and southwest of the storm, and persistent convection over the center.  The Clean Window animation over the same time, below, shows a compact center with periodic overshooting tops.

GOES-16 Clean Window Infrared Imagery (Band 13, 10.3 µm), from 1837 – 2332 UTC on 8 July 2018 (Click to animate)

The toggle below between 2212 UTC on 6 and 8 July shows the general increase in organization of Chris, with a slight northwestward motion over the two days. In addition, the front that was over the eastern United States on 6 July is out over the Atlantic on 8 July, and Chris is embedded within the southwestern tail of the front.

GOES-16 Visible Imagery (Band 2, 0.64 µm), at 2212 UTC on 6 July and 8 July 2018 (Click to enlarge)

Tropical Depression #3 forms off the East Coast of the United States

July 6th, 2018 |

GOES-16 Visible Imagery (Band 2, 0.64 µm), from 1712 – 2212 UTC on 6 July 2018 (Click to animate)

Tropical Depression Three has formed in the Atlantic Ocean southeast of Cape Hatteras. The visible animation above (click the image to play an animated gif) shows strong convection with overshooting tops mostly south and west of a low-level circulation. The cold front over the eastern United States, and an upper-level Low that is moving inland over Florida, are also apparent. Because the depression is within GOES-16’s CONUS Domain, 5-minute imagery is available to monitor this system.

A variety of GOES-16 images and products can be used to discern whether this storm will develop (The National Hurricane Center suggests slow motion and slow development: Click here for details).

The low-level Water Vapor field, below (7.34 µm) from 2122 UTC, shows little dry air in the path of the storm. The Total Precipitable Water derived from GOES-16 ABI data similarly shows rich moisture surrounding the storm.

GOES-16 Low-Level Water Vapor (Band 10, 7.34 µm), 2212 UTC on 6 July 2018 (Click to enlarge)

GOES-16 Clean Window Infrared (Band 13, 10.3 µm) imagery superimposed upon GOES-16 Estimates of Total Precipitable Water, 2212 UTC on 6 July 2018 (Click to enlarge)

GOES-16 Estimates of Sea Surface Temperature, below, color-enhanced such that waters warmer than 27 º C are violet, shows warm surface waters. Gulf Stream temperatures, northwest of the Depression, are at 30-31 º C.

GOES-16 Estimates of Sea Surface Temperature, 2100 UTC on 6 July 2018 (Click to enlarge)

For more information on this system, please see the website of the National Hurricane Center and the CIMSS Tropical Weather Website.

Tropical Storm Beryl forms in the Atlantic Ocean

July 5th, 2018 |

GOES-16 Band 2 (“Red Visible”, 0.64 µm) Imagery over the Atlantic Ocean, 0915-2130 UTC on 5 July 2018 (Click to animate)

The season’s second named tropical cyclone in the Atlantic Basin has formed.  GOES-16 visible imagery, above (click to play an animated gif), shows Tropical Storm Beryl moving westward just north of 10 º N Latitude between 40 º and 50 º W Longitude.  The infrared imagery (10.3 µm), the Clean Window, below shows a compact storm with cold cloud tops and a central dense overcast.

GOES-16 Band 13 (“Clean Window”, 10.3 µm) Infrared Imagery over the Atlantic Ocean, 0915-2130 UTC on 5 July 2018 (Click to animate)

Much of the tropical Atlantic north of 10 N Latitude shows little convection.  This is because of a Saharan Air Layer, shown below (in red) from a screen capture from the CIMSS Tropical Website (Click here for the latest SAL analysis). An important component of the SAL analysis is the Split Window Difference field (10.3 µm – 12.3 µm) that can diagnose both moisture and dust. The SAL analysis shows considerable dry Saharan air over the Atlantic; Beryl has formed along its southern edge. Compare the SAL analysis to the Split Window Difference field, below, that shows dry air in blue. Similar features are present in both. The GOES-16 Low-Level Water Vapor Infrared Imagery (7.34 µm), here, shows similar features as well. There are multiple ways to diagnose dry air with GOES-16.

Saharan Air Layer (SAL) Analysis, 2100 UTC on 5 July 2018 (Click to enlarge)

GOES-16 Split Window Difference field (10.3 -12.3 µm) Imagery over the Atlantic Ocean, 2100 UTC on 5 July 2018 (Click to enlarge)

NUCAPS Soundings from Suomi NPP can be used to diagnose the thermodynamics of the atmosphere surrounding Beryl. The image below shows NUCAPS Soundings locations between 1500 and 1600 UTC on 5 July 2018, and the points are color-coded to describe the data (as discussed here). A Sounding near 16.3 N, 43.1 W (north of Beryl) shows dryness at mid-levels; total precipitable water is only 1.27″. A Sounding closer to the storm, at 10.3 N, 43.5 W (west of Beryl) is much wetter: total precipitable water is 2.12″. NUCAPS Soundings are available online (over the Continental US only) here.

NUCAPS sounding locations over Beryl at 1500-1600 UTC on 5 July 2018 (Click to enlarge)

Very small (in size) Beryl is forecast to strengthen in the short term. See the National Hurricane Center website and the CIMSS Tropical Website for more information.


==== Update 6 July 2018 ====
Beryl has strengthened and is a hurricane, as of 0900 UTC on 6 July, the first hurricane of the 2018 Atlantic Hurricane season. The sandwich product animation below, courtesy Rick Kohrs and Joleen Feltz, CIMSS, that combines visible (0.64 µm) and clean window infrared (10.3 µm) imagery shows the appearance and subsequent disappearance of a very small eye.

Sandwich product that combines GOES-16 Band 2 (“Red Visible”, 0.64 µm) and Band 13 (“Clean Window”, 10.3 µm) over Beryl, 0815-1515 UTC on 6 July 2018 (Click to enlarge)

Fixed-Grid Format Data flowing in AWIPS

June 19th, 2018 |

AWIPS imagery of GOES-16 Low-Level Water Vapor (7.34 µm) at 1527 and 1532 UTC on 19 June (Click to enlarge)

Until today, GOES-16 Data that flowed into AWIPS was remapped twice: First, from the observational perspective (that is, how the satellite views it) to a spherical fixed-grid projection that approximates the Earth, and then to a Lambert Conformal projection with (for infrared data) 2-km resolution over the Globe. That Lambert Conformal data was then shipped to AWIPS, where the data were again re-projected into the observational perspective desired by the meteorologist.

The 2-km resolution of the data shipped to AWIPS before today is applicable only at the sub-satellite point (nadir) for GOES-16. Thus, the second remap was suggesting better resolution than was warranted by the data. Additionally, the number of data points needed to be sent was very big.

At 1532 UTC on 19 June, the first fixed-grid format data were directly shipped to AWIPS; remapping to a Lambert Conformal projection is no longer done upstream of AWIPS. The toggle above shows the difference in the 7.34 µm “Low-Level” Infrared Water Vapor imagery over the coast of Oregon, near 46º N, 124º W (very far from the GOES-16 sub-satellite point at 0º N, 75.2º W), in the AWIPS CONUS projection.  At 1532 UTC, after the double remap is removed, the pixels are more distinct, and as expected they splay away from the sub-satellite point.

Removing a remapping in the data processing means that pixel-sized extremes — such as overshooting tops, or fires — and gradients will be better represented in the data.  Consider the Clean Window (10.3 µm) Infrared imagery below of strong convection over the Gulf of Mexico east of Texas.  Overshooting tops Brightness Temperatures are colder and the tops themselves more distinct after 1532 UTC than at 1527 UTC.

AWIPS imagery of GOES-16 Clean Window Infrared Data (10.3 µm) from 1347 to 1612 UTC on 19 June. The animation pauses on the last double-remapped image at 1527 UTC, and the first fixed-grid format image at 1532 UTC (Click to enlarge)

 

See also this blog postThis training also discusses the remapping.  And here (or here) is the National Weather Service announcement on the change.