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 1

c) The Eastern Pacific Tropical System

Refer to the following Table 1 that 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

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, 40kn

Oct 21, 1500

11.8

103.5

Hurricane

987 hPa, 65 kn

Oct 22, 0300

12.0

105.5

Hurricane

981 hPa, 70 kn

Oct 22, 2100

12.3

108.4

Storm

994 hPa, 55 kn

Oct 23, 0300

12.5

109.0

Storm

997 hPa, 50 kn

Oct 24, 1500

14.5

113.1

Storm

1002 hPa, 40kn

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 -- 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?

Discussion

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 knots. 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 knots (994 hPa/55 kn 3 hours before the initialization and 997 hPa/50 kn 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 short waves in the westerlies over the Pacific that can be expected to move “over” the western North American long wave ridge and to “drop into” the long wave trough over the eastern U.S. (See questions A, B, and C above). 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 short wave troughs initially in the Pacific.