Homework 2: Hurricane Katrina. Part 1. Hurricane Katrina, August 28, 2005 Satellite Imagery

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1 Metr 302 Homework 2 Fall 2014 Meteorology 302 Fall 2014 Name Homework 2: Hurricane Katrina 100 points total Distributed Thursday 30 October 2014; Due Thursday 13 November 2014 Answer all questions in complete sentences ON THE BACK OR ON SEPARATE SHEETS OF PAPER. Questions which require a "yes" or "no" answer should also have an explanatory sentence explaining reasoning. Many of the questions below simply have you OBSERVE something. Yet you still need to put your observation in the context of a complete sentence. Note: There are six parts to the homework, each with a short set of one or more questions underneath the images you are asked to examine. You do not have to print out the images. But click on the images surrounded by the blue boxes to see larger, more readable versions. Part 1. Hurricane Katrina, August 28, 2005 Satellite Imagery (Left) 2215 UTC 8/28/05 visible image of Katrina (1 km resolution), and (Right) Enhanced infrared image of Katrina (4 km resolution) Questions: Compare the two images, which are for 2215 UTC 8/25/05. Note the portions of the images labeled A and B (the same locations at the same times for both images). Answer the following questions. 1. What evidence do you see on the INFRARED image that the clouds at the two locations are probably cumulonimbus? (6 pts) The coldest cloud tops are associated with the two locations. The red color indicates temperatures of around -70C. Cold temperatures can be associated with towering clouds, such as cumulonimbus. 2. What evidence do you see on the VISIBLE image that the cloud at A is cumulonimbus? (6 pts) The area labeled A is towering so high above the surrounding overcast that it is casting a shadow. This means that the top of the cloud is much taller than the surrounding cloud mass, and is probably associated with a cumulonimbus. 3. In general, with respect to the center of the storm, where would you expect the heaviest precipitation to be occurring and why? (8 pts)the coldest cloud tops appear to be around the center of the storm, as Page 1 of 6

2 mentioned in answer to (1) above. Thus, towering cloud forms, usually associated with heavy precipitation, should be occuring around the center of the storm. Part 2. Hurricane Katrina, Surface Weather Map Surface Weather Map, 16 UTC 29 August 2005 Questions: 1. Describe what you see on the surface weather map that would suggest that strong winds would be occuring in the north-central Gulf of Mexico coastal sections, EVEN IF NO SURFACE OBSERVATIONS WERE PLOTTED. (10 pts)the isobars are very close together. This suggests that the wind speeds would be very high in that location. 2. Examine the weather information for Mobile, Alabama. Describe how the (a) dew point temperature; (b) wind speed; and, (c) atmospheric pressure were unusual (compared to the kind of values we have seen so far this semester on the surface weather map). (15 pts) The dew point temperature of 76F is higher than any dew point we have seen on a weather map in this class, and much greater than the 60F dew point we've discussed as being a threshold for thunderstorms.. The sustained wind speed is 50 mph, which is also the highest sustained wind speed we have seen on a surface weather map, as well as being excessively strong for a sustained wind speed at sealevel. Finally, the atmospheric pressure is mb, which is also far lower than average pressure of mb and also far lower than we have seen on a weather map in this class. Page 2 of 6

3 Part 3. Hurricane Katrina, Mobile Meteogram Questions: Meteogram for Mobile, Alabama: 05 UTC 29 August to 05 UTC 30 August Give the date and time at which the center of Katrina passed closest to Mobile, and how did you tell. (7 pts) The lowest pressure was observed around 17 UTC (12:00 PM CDT) on 29 August. Since hurricanes are surface thermal low pressure areas, this appears to be the time that the storm was closest to Mobile. Also, the strongest winds occurred at that time. 2. What was the date and time of the peak wind gust, and what was its strength and direction? (5 pts) The peak wind gust was southeast at 69 mph, and that was observed at 18 UTC (1 PM CDT) on 29 August. 3. The chief problems in the Mobile region with the passage of Katrina was something called the "storm surge" and not the wind, or the rainfall associated with the storm. What was the strongest sustained wind, and how much rainfall occurred at Mobile over the 24 hour period shown? (8 pts) The strongest sustained wind was southeast at 50 mph, and that was observed at 16 UTC (12:00 PM CDT) on 29 August. 3.80" (4.22" is OK too) of rainfall occured during the 24 h period. Part 4. Hurricane Katrina, New Orleans Radar Animation Page 3 of 6

4 Questions Animation of radar imagery from the New Orleans Doppler Radar (KLIX) 1. In general, in what direction was Katrina itself moving as it was affecting the city of New Orleans? (5 pts) Katrina appeared to be moving slightly west of north as it was affecting New Orleans. 2. In general, how were the precipitation areas associated with Katrina moving with respect to the storm itself (clockwise or counterclockwise)? (5 pts) The rain areas appear to be moving counterclockwise with respect to the center of the storm. 3. In general, where was the heaviest precipitation/strongest thunderstorm activity located with respect to the center of the storm? (5 pts) The heaviest precipitation, indicated by the oranges and red colors, are found around the center of the storm, with a greater concentration suggested north of the center, over New Orleans. The colors indicate heaviness of precipitation, with reds, yellows and purples indicating the heaviest precipitation. This is consistent with my answer in Part 1 above. 4. How does the radar animation corroborate the fact that hurricanes are cyclones? (4 pts) Cyclones are low pressure areas with the center completely enclosed by at least one isobar. Wind should move counterclockwise around such pressure systems. The radar animation shows that the rain bands are moving counterclockwise. Assuming that the rainfall areas are associated with clouds whose motion is directed by the winds, then the winds are moving counterclockwise. In addition, the rainfall areas are making a complete circuit around the center of the disturbance, consistent with the fact that at least one isobar encircles the center. Part 5. Hurricane Katrina, Track Forecast, and NHC Advisory Page 4 of 6

5 Actual track of Katrina (left) and (right) forecast track as of August 26, The blue hurricane symbols represent the actual position of Katrina at 6 hour intervals. The black hurricane symbols indicate the forecast future positions of the storm at 12 hour intervals. The chart at left shows the track of Katrina just as it was making landfall near New Orleans. The right hand chart shows the forecast that was made when Katrina was just north of Key West, Florida, on August 26, nearly 3 days before it made landfall. ZCZC MIATCPAT2 ALL TTAA00 KNHC DDHHMM BULLETIN HURRICANE KATRINA ADVISORY NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 10 PM CDT SAT AUG DANGEROUS HURRICANE KATRINA THREATENS THE NORTH CENTRAL GULF COAST...A HURRICANE WARNING ISSUED... AT 10 PM CDT Z...A HURRICANE WARNING HAS BEEN ISSUED FOR THE NORTH CENTRAL GULF COAST FROM MORGAN CITY LOUISIANA EASTWARD TO THE ALABAMA/FLORIDA BORDER...INCLUDING THE CITY OF NEW ORLEANS AND LAKE PONTCHARTRAIN. A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED WITHIN THE WARNING AREA WITHIN THE NEXT 24 HOURS. >PREPARATIONS TO PROTECT LIFE AND PROPERTY SHOULD BE RUSHED TO COMPLETION. FORECASTER PASCH National Hurricane Center Advisory #19 (10 PM CDT Saturday August 27, 2005) "...Nonetheless, top officials at every level of government despite strongly worded advisories from the National Hurricane Center (NHC) and personal warnings from NHC Director Max Mayfield did not appear to truly grasp the magnitude of the storm s potential for destruction before it made landfall..." from "Hurricane Katrina: A Nation Still Unprepared" S. Rept , Congressional Report from the Committee on Homeland Security. Questions 1. Based upon your examination of the two charts showing the actual track and forecast track, evaluate the relative accuracy of the predictions made on August 26 (chart at right). (5 pts)the path of Katrina was well forecast, as was its approximate Page 5 of 6

6 Metr 302 Homework 2 Fall 2014 arrival time in the coastal sections of Lousiana, Mississipi and Alabama. There was about 2 1/2 to 3 days warning. 2. Katrina made landfall on Monday August 29. Hurricane Advisory #19 above was the last of many made in the days between 25 and 27 August regarding Katrina just as Hurricane Warnings were issued. In your view, if this statement was consistent with the others issued, was the conclusion of the Congressional Report justified? (5 pts) Since there was about 2 1/2 to 3 days warning to the Gulf Coast, and this warning contained very strong language, it appears that if there was a lack of preparedness, it was not due to the actions of the National Weather Service, and the conclusion of the congressional report was justified. Part 6. Hurricane Katrina, Intensification Gulf of Mexico sea surface temperatures and position of Loop Current on August 27, 2005 (left) and (right) actual track history of Katirna with red colors show period of Category 5. Other colors (orange, Category 4; Yellow Category 3; White Category 2). Question (10 points) Based upon your examination of the two charts comment on the intensification of Katrina after it moved across southern Florida.The path of Katrina took it across the warmest waters of the Loop Current. Hence greatest intensitifcation occurred when it was over the warmest temperatures and, presumsedly, the highest dew points (from ocean evaportation). Both of these factors would contribute intensification of a surface thermal low. Page 6 of 6