CIMSS Satellite Blog

While the Atlantic Ocean tropical cyclone season has been relatively quiet thus far, the Eastern Pacific Ocean was showing some signs of activity in late June 2008. Products from the CIMSS Tropical Cyclones site such as AMSU brightness temperature (above) and Satellite Consensus (SATCON) tropical cyclone intensity estimates (below) were useful to forecasters at the National Hurricane Center, as noted in their Tropical Storm Boris discussion from 29 June 2008:

TROPICAL STORM BORIS DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

800 PM PDT SUN JUN 29 2008

THE RAGGED EYE VISIBLE EARLIER HAS BEEN OBSCURED BY NEW CONVECTION NEAR THE CENTER…ALTHOUGH EXCELLENT BANDING ALOFT IS APPARENT IN AN AMSU PASS AT 0045 UTC. THE ADVISORY INTENSITY OF 60 KT IS A BLEND OF SUBJECTIVE DVORAK ESTIMATES OF 55 KT FROM TAFB AND SAB…A CIMSS ADT OF 65 KT…AND A CIMSS AMSU ESTIMATE OF 66 KT.

Not far to the west of Boris, Tropical Storm Cristina was also present over the Eastern Pacific Ocean. ASCAT satellite wind vectors were helpful in verifying the intensity of Cristina, as seen in on GOES-11 visible and IR imagery with ASCAT data superimposed (below).

A 30 June 2008 National Hurricane Center discussion for Tropical Storm Cristina also noted

TROPICAL STORM CRISTINA DISCUSSION NUMBER 11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

200 AM PDT MON JUN 30 2008

THE CLOUD PATTERN ASSOCIATED WITH CRISTINA HAS BECOME LESS ORGANIZED OVER THE PAST SEVERAL HOURS. THERE IS A RATHER SHARP EDGE TO THE HIGH CLOUD MASS OVER THE EASTERN SIDE OF THE SYSTEM…INDICATIVE OF EASTERLY VERTICAL SHEAR. THIS SHEAR IS AT LEAST PARTIALLY DUE TO THE UPPER-LEVEL OUTFLOW FROM TROPICAL STORM BORIS LOCATED NOT FAR TO CRISTINA’S EAST.

This sharp eastern cloud edge was quite evident on GOES-11 IR imagery (below), which also displays the CIMSS wind shear product.

One factor influencing the lack of organized tropical storm activity in the Atlantic so far this season may have been the persistent Saharan Air Layer and airborne African dust that was frequently observed over the tropical Atlantic basin during the month of June 2008 — note the presence of significantly lower MIMIC Total Precipitable Water (TPW) values during the 27-30 June 2008 period (below) within the 10-20º N latitude band over the Atlantic Ocean, compared to the much higher TPW values over tropical East Pacific where Tropical Storms Boris and Cristina were seen. One impact of such a high amount of African dust may be the cooler than normal Sea Surface Temperatures across the tropical Atlantic, which would be a negative factor for tropical cyclone formation.

Just 11 days after deadly Cyclone Nargis made its devastating landfall in Myanmar (also known as Burma), Meteosat-7 IR imagery from the CIMSS Tropical Cyclones site (above) showed a new tropical disturbance that was moving northwestward across the Irawaddy Delta region of Myanmar on 13 May 2008. The Joint Typhoon Warning Center issued the following Tropical Cyclone Formation Alert at 20:30 UTC:

WTIO21 PGTW 132030
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 150 NM EITHER SIDE OF A LINE FROM 16.5N 96.1E TO 19.4N 92.1E WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 25 TO 30 KNOTS. METSAT IMAGERY AT 131800Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 16.7N 95.7E. THE SYSTEM IS MOVING WEST-NORTHWESTWARD AT 06 KNOTS.
2. REMARKS: RECENT ANIMATED INFRARED SATELLITE IMAGERY AND A 121210Z SSMI MICROWAVE IMAGE INDICATE PRONOUNCED LOW-LEVEL CYCLONIC TURNING OF CONVECTION AT THE WESTERN END OF THE MONSOON TROUGH. HOWEVER, MORE RECENTLY, CONVECTION HAS WANED SOMEWHAT IN RESPONSE TO LAND INTERACTION. THE CIRCULATION CENTER IS CURRENTLY TRANSITING
GENERALLY NORTHWESTWARD ACROSS THE YANGON DELTA REGION OF MYANMAR. OBSERVATIONS FROM YANGON AS OF 131300Z, SUPPORT A 25 TO 30 KNOT CIRCULATION WITH SEA LEVEL PRESSURES NEAR 1000 MB (3 MB PRESSURE FALLS OVER THE PAST 24 HOURS) AND SUSTAINED WINDS AT 10 KNOTS GUSTING TO 20 KNOTS OUT OF THE NORTHEAST. A PARTIAL 130301Z ASCAT
IMAGE ALSO INDICATES STRONG WESTERLIES TO THE SOUTH OF THE CENTER WITH SUSTAINED EASTERLIES TO THE NORTH, FURTHER PROOF OF CYCLONIC TURNING. THE CENTER CURRENTLY LIES UNDER LOW VERTICAL WIND SHEAR JUST SOUTH OF THE SUBTROPICAL RIDGE AXIS WITH FAVORABLE SOUTHWESTERLY DIFFLUENCE ALOFT. THOUGH THE DISTURBANCE IS CURRENTLY OVER LAND, MINIMAL DEGRADATION OF THE LOW LEVEL IS EXPECTED DUE TO THE LOW LYING TOPOGRAPHY AND FAIRLY QUICK TRANSIT
OVER THE LOW-LYING COASTAL REGION OF SOUTHERN MYANMAR. EMERGENCE INTO THE BAY OF BENGAL IS EXPECTED WITHIN THE NEXT 12 TO 18 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS GOOD WITH THE ONLY LIMITATION BEING TEMPORARY LAND INTERACTION.

CIMSS satellite-derived atmospheric motion vectors and products (below) indicated that the upper-tropospheric winds, divergence, and deep layer shear were all relatively weak  over the region at that time.

Severe convection along an advancing cold frontal boundary was responsible for several tornadoes and reports of damaging winds across southeastern Virginia on 28 April 2008 (SPC storm reports | Wakefield, Virginia NWS forecast office storm report). AWIPS images of the GOES-12 10.7 µm IR channel data (above) showed that cloud top brightness temperatures began to cool into the -55 to -65º C range (orange to red enhancement) after about 18:15 UTC (2:15 PM local time), but no classic severe storm signatures such an “enhanced-v” were noted. The strongest tornado moved through the Suffolk, Virginia area during the 20:05 - 20:15 UTC (4:05 - 4:15 PM local time) period, producing EF-3 damage (about 140 homes were either destroyed or damaged) and injuring over 200 people.

A comparison of 4-km resolution GOES-12 IR and 1-km resolution NOAA-18 IR images (below) revealed an area of cold cloud top brightness temperatures between Petersburg (KPTB) and Emporia (KEMV) in southeastern Virginia around 18:40-18:45 UTC (2:40-2:45 PM local time), close to the time that a tornado (denoted by “TOR” on the images) produced EF-1 damage near Lawrenceville, Virginia. Cloud top brightness temperatures were several degrees colder on the NOAA-18 IR image (-61º C, vs. -56º C on the GOES-12 IR image), but still rather unremarkable compared to the -70 to -80º C values that are often seen associated with severe convection in the Plains states. As discussed in the Jon Davies Severe Weather Notes blog, the atmosphere over southeastern Virginia on that day exhibited relatively weak instability (which was confined to low levels), which likely limited the resulting thunderstorm updraft intensities — stronger updrafts would probably have produced significantly colder satellite IR temperatures associated with the overshooting tops.

Hourly images of the MIMIC Total Precipitable Water (TPW) product from 28 April (below) showed that a plume of relatively high TPW (35-45 mm or 1.4-1.8 inches, light blue to green to yellow enhancement) originating over the Gulf of Mexico was streaming northeastward along the Eastern Seaboard during the day, helping to provide the necessary moisture for convective development along and ahead of the cold front that was moving eastward through the mid-Atlantic states.

AWIPS image combinations of the DMSP TPW + GOES-12 sounder TPW (below) also show the TPW plume, and include an overlay of the GOES-derived atmospheric motion vectors. These satellite winds showed that a large trough was centered over the southern Great Lakes and Ohio River Valley; in addition, a diffluent flow pattern within the upper troposphere (the 450-275 mb layers, green and cyan wind vectors) was evident over eastern Virginia. This diffluence aloft likely contributed to the creation of an environment that supported large-scale ascent favorable for severe thunderstorm  development over that particular region during the afternoon hours on 28 April.