Part I: Medium Range Forecast Exercise for Tallahassee, Florida

Medium Range Forecast Exercise for Tallahassee, Florida:
A Prototype for Forecasting along the Gulf Coast in Fall

Part I, Section 1c: The Eastern Pacific Tropical System

Refer to Table 1, which outlines a brief history of the named tropical system in the eastern Pacific, Patricia, which was a tropical storm at the time of the model initializations for 0000 UTC 23 October 2003. Note that the system reached its maximum intensity on October 22 at 0300 UTC and that the two closest times to the model initializations are October 22 at 2100 UTC and October 23 at 0300 UTC.

Table 1: Data for Eastern Pacific Tropical System Patricia

Date, Time (UTC)

Latitude (°N)

Longitude (°W)

Classification

Press., Wind

Oct. 20, 1630

100.7

Depression

Oct. 20, 2100

10.5

101.7

Storm

1002 hPa, 40 kts>

Oct. 21, 1500

11.8

103.5

Hurricane

987 hPa, 65 kts

Oct. 22, 0300

12.0

105.5

Hurricane

981 hPa, 70 kts

Oct. 22, 2100

12.3

108.4

Storm

994 hPa, 55 kts

Oct. 23, 0300

12.5

109.0

Storm

997 hPa, 50 kts

Oct. 24, 1500

14.5

113.1

Storm

1002 hPa, 40 kts

Oct. 25, 1500

15.6

113.9

Depression

Oct. 26, 0300

16.2

114.9

Depression

For your convenience, we show Figures 1 and 2 again—the GFS and UKMET initializations.

Figure 1: GFS 500 hPa height (orange) and absolute vorticity (green) in the initialization for 0000 UTC 23 October 2003

Figure 2: UKMET 500 hPa height (orange) and absolute vorticity (green) in the initialization for 0000 UTC 23 October 2003

Question D, Part I, Section 1c

After examining the data in Table 1, do you think that Patricia is a possible player in the day-5 forecast for TLH ? Which of the following statements are reasonable in this regard? Choose all choices that apply, then click Done. (To undo a selection, click the choice again.)

Discussion

Answers a) and d) are correct. Twenty-one hours before the initialization of 0000 UTC 23 October 2003, Patricia was a hurricane with a central pressure of 981 hPa and maximum sustained winds of 70 kts. At the time of the initialization, the system had weakened to a tropical storm with a central pressure still below 1000 hPa and maximum sustained winds of between 50-55 kts (994 hPa/55 kts 3 hours before the initialization and 997 hPa/50 kts 3 hours after the initialization). Even though the system is weakening, it still represents an important atmospheric circulation with large amounts of associated moisture. Such a late season tropical system has the potential to be picked up by the westerlies and to have its moisture influence the weather over the U.S. in the medium range. Recall that in this particular synoptic setting, there are two strong shortwaves in the westerlies over the Pacific that can be expected to move over the western North American longwave ridge and to drop into the longwave trough over the eastern U.S. (See previous Questions A, B, and C). Such troughs have the potential to pick up the residual moisture from Patricia and to carry that moisture into the U.S. Thus, Patricia should be considered a potential player for the day-5 forecast for TLH.

		a) The system is initially intense enough to allow for an influence on the day-5 forecast.
		b) The system is too weak to have any influence on the day-5 forecast.
		c) The system is too far to the south and west to have any influence on the day-5 forecast.
		d) Residual moisture from the system could be brought northward by shortwave troughs initially in the Pacific.

Medium Range Forecast Exercise for Tallahassee, Florida: A Prototype for Forecasting along the Gulf Coast in Fall

Question D, Part I, Section 1c

Medium Range Forecast Exercise for Tallahassee, Florida:
A Prototype for Forecasting along the Gulf Coast in Fall