Tropical Storm Isaac Track Chart, Advisory #20

Current Location: 15.0N, 54.4W
Geographic Reference: 435 miles east of Martinique
Movement: West at 21 mph
Max Winds: 60 mph gusting to 75 mph
Current Hurricane Severity Index: 5 out of a possible 50 points (2 size, 3 intensity)
Max Predicted Hurricane Severity Index: 5 out of a possible 50 points (2 size, 3 intensity)
Current Radius of Tropical Storm-Force Winds: 75 miles
Max Predicted Radius of Tropical Storm-Force Winds: 75 miles
Organizational Trend: Steady
Forecast Confidence: Average

Key Points
1. Isaac is predicted to strike the central Lesser Antilles as a tropical storm tomorrow morning.
2. Weakening and dissipation are forecast to occur in the Caribbean due to strong wind shear.
3. The remnants of Isaac are unlikely to reach the Gulf of Mexico next week.

Our Forecast
Isaac has not changed much over the past few hours. The low level center is exposed near the northwestern edge of the associated squalls. Though the maximum sustained winds remain near 60 mph, gradual weakening is expected very soon. The reconnaissance plane currently investigating Isaac is having difficulty finding any tropical storm force winds near the center. The strongest winds so far have been found well to the north. We are forecasting Isaac to still be a tropical storm when it moves through the Lesser Antilles in about 24 hours. However, there is a chance it will have already weakened to a depression by that time.

Expected impacts on Land
Central Lesser Antilles: Scattered power outages are expected within about 70 miles of the center. Flooding and mudslides are likely to cause some damage and travel delays.

Puerto Rico : At this time, most of the rain and all of the wind associated with Isaac are expected to pass the island to the south. However, Isaac could track close enough to the island to bring an increased chance of showers and thunderstorms on Friday.

Our next advisory will be issued by 4 PM AST / 3 PM CDT.

Meteorologist: Jim Palmer

Forecast Confidence:   Average Hurricane Severity Index
Fcst Hour Valid Lat. Lon. Max Sustained Winds Max Gusts Category Size Intensity Total
0 9AM CDT Wed Sep 12 15.00N 54.40W 60 mph 75 mph Tropical Storm 2 3 5
12 9PM CDT Wed Sep 12 15.00N 58.10W 50 mph 65 mph Tropical Storm 1 2 3
24 9AM CDT Thu Sep 13 15.10N 61.50W 50 mph 70 mph Tropical Storm 1 2 3
36 9PM CDT Thu Sep 13 15.30N 64.80W 50 mph 65 mph Tropical Storm 1 2 3
48 9AM CDT Fri Sep 14 15.30N 67.90W 45 mph 60 mph Tropical Storm 1 2 3
60 9PM CDT Fri Sep 14 15.40N 70.70W 40 mph 50 mph Tropical Storm 1 1 2
72 9AM CDT Sat Sep 15 15.50N 73.10W 40 mph 50 mph Tropical Storm 1 1 2
84 9PM CDT Sat Sep 15 15.60N 75.10W 35 mph 45 mph Tropical Depression 0 1 1
96 9AM CDT Sun Sep 16 15.80N 77.00W 30 mph 40 mph Remnant Low 0 0 0

The yellow cone represents track error from the previous five hurricane seasons. Over the past five hurricane seasons, the center of the storm tracked within the yellow cone 75% of the time. The cone does not represent the forecast uncertainty in the current advisory for this storm. In addition, hurricane-force winds, very high tides, large waves, and heavy rainfall can often extend well outside the yellow cone.