ISNS2368_Homework_10_ Hurricanes(2) - Tagged
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Date
Dec 6, 2023
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ISNS2368 Homework #10: Hurricane Sandy
Hurricane Sandy initially formed in the Caribbean Sea on October 22, 2012, and moved generally
northward until October 29, when it suddenly took a left-hand turn and moved northwest. It made
landfall in New Jersey that evening and eventually dissipated near Lake Eerie on October 31.
The map below shows the path that Sandy took for the period from 1200 Z October 22 through 1200Z
October 31.
“Z” is called Zulu Time which is the same thing as Universal Coordinated Time which is the
same thing as GMT Greenwich Mean Time.
To convert Z time to CDT (Central Daylight Time) you would
subtract
5 hours.
To convert to CST (Central Standard Time) you would subtract 6 hours.
Since Daylight Saving Time is in effect during the month of October, the map below shows the path that
Sandy took for the period from 7:00 AM CDT October 22 through 7:00 AM CDT October 31.
The Track of Sandy. The white circles are the storm's positions at 12z (7:00
A
.
M
. CDT)
The graph below shows how Sandy’s central air pressure and maximum winds changed over time.
Central Air Pressure and sustained wind speed of Sandy from 0Z 22 Oct to 12Z 31 Oct
(Note: 06Z would be the time halfway between 0Z and 12Z)
For example, the chart above tells us that at 0Z on October 22 (which would be 7 PM October 21 CDT),
the air pressure in the center of the cyclone was 1005 mb, and the sustained wind speed at that time
was about 30 mph.
Therefore, Sandy had not yet even been given a name at this time since the winds
were not yet at 39 mph which is needed to qualify for tropical storm status.
Another example:
For the period from 0Z 28 October through 18Z 28 October, the air pressure dropped
from
960 mb to
952 mb, and the wind speed stayed constant at 75 mph.
Make sure you understand the two examples above.
This will let you know if you are interpreting the
graph correctly in order to answer the questions below.
(1)
What is the relationship between the air pressure reading and the observed wind speed? In other
words, as the central air pressure goes down, what does the wind speed do?
Or, if the central air
pressure goes up, what does the wind speed do?
(2)
According to the wind speed data above, approximately when did Sandy get her name (i.e., tropical
cyclones get named when their sustained winds reach 39 mph)?
(3)
According to the wind speed data above, approximately when did Sandy become a hurricane(i.e.,
tropical cyclones are upgraded to hurricane status when sustained winds reach 74 mph)?
(4)
According to the wind speed data on the previous page, approximately when did Sandy become a
MAJOR hurricane (i.e., hurricanes are considered MAJOR when they reach 111 mph sustained winds)?
The image below
shows Hurricane Sandy’s path across eastern Cuba on October 25 for the 4-hours-and-
35-minute period from 0525 Z to 1000 Z. Also indicated are the lowest surface pressure readings,
maximum sustained winds, and maximum wind gusts at selected weather stations on the island during
this period of time.
For example, the data plotted for the city of Guantanamo in SE Cuba show that the lowest pressure was
990.4 mb
, the highest SUSTAINED wind was
46 mph
, and the highest GUST of wind was
76 mph
.
(5)
Knowing that winds spin
counterclockwise
in a hurricane in the northern Hemisphere, what was the
likely wind direction at Guantanamo at 0600 Z?
(6)
What was the likely wind direction at Contramaestre at 0800 Z?
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(7)
At approximately what time would the eye of the storm pass directly over Guaro which would cause
the winds to go nearly calm?
(8)
Knowing that Hurricane Sandy was spinning counterclockwise while moving north, explain why the
winds on the right side of Sandy were stronger than the winds on the left side.
Hurricane Forecasting
The National Hurricane Center issues official hurricane forecasts, watches, and warnings from data taken
by reconnaissance planes, buoys, satellites, and radar.
These data go into computer programs that
attempt to predict the path a hurricane will take and where the hurricane will make landfall. The graph
below shows the average error in the forecasted hurricane paths for forecasts that go out 24, 48, and 72
hours into the future.
For example, in 1970, the average error in the forecast position of a hurricane 24 hours into the future
was about 150 km which is about 80 nautical miles (nm). For the same year, the average error in the
forecast position of a hurricane 48
hours into the future was about 350 km which is about 190 nautical
miles.
And finally, the average error in the position of a hurricane 72 hours into the future was about
475 km which is about 255 nm.
Average hurricane track errors, 1970–2004
(9)
Describe how the 24-hour, 48-hour, and 72-hour forecasts hurricane paths have changed over time in
terms of the error.
Remember to write about each specific forecast time period in your response.
In
other words, make sure you mention the 24-hour forecast error trend, the 48-hour forecast error trend,
and the 72-hour forecast error trend.
(10)
Why do you think the forecast position of a hurricane 72 hours into the future has significantly more
error than the 24-hour forecast?
The four maps below and on the next page show a variety of predicted paths (i.e., spaghetti plots)
Hurricane Katrina was expected to make from August 25 through August 28. The forecasts go out 72
hours for each of these dates. This means the end of each line is the expected position of Katrina by the
end of the 72-hour period.
Each
dotted line
in these maps indicates the predicted path made by 5
different computer weather forecast models. The
solid line
represents the National Hurricane Center’s
official forecast track.
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(11)
How would you describe the various forecast paths made by the COMPUTER weather forecast
models on August 25 (i.e., the first map in this series)?
(12)
How would you describe the various forecast paths made by the COMPUTER weather forecast
models on August 28 (i.e., the last map in this series)?
How Good Was the Forecast?
For the last 20 years, the National Hurricane Center's 24-hour forecast for the position of a hurricane has
an average error of 140 kilometers (87 miles). This means that the predicted position of a hurricane 24
hours into the future was wrong by an average of 140 km (87 miles). At 48 hours, the average error is
approximately 255 kilometers (158 miles).
Examine the 24-hour and 48-hour forecasts made by the National Hurricane Center and the actual path
Katrina took on the maps below.
The official forecast by the NHC is indicated by the
SOLID BLACK LINE
,
and the actual path Katrina took is indicated by the dashed line.
(13)
How did the NHC prediction for this storm compare to the average errors for the 24-hour and 48-
hour time periods? Use the MAP SCALE in the lower left to assist you in answering this question!
(14)
Locate New Orleans, LA and Biloxi, Mississippi on a map from the Internet.
Given Katrina’s
northward movement, which city would have the strongest winds
and WHY?