Hurricane Irene Advisory, August 24, 2011 (8 PM EDT)

Miami, Florida—(ENEWSPF)—August 24, 2011 – UPDATE 8 PM EDT eNews Park Forest continues to post raw data regarding hurricane Irene to keep the public informed as quickly as possible.


The satellite presentation of the hurricane has continued to improve this afternoon. A large area of deep convection with very cold cloud tops has expanded near the eyewall and now solidly surrounds the eye. Before departing Irene…the air force reserve hurricane Hunter aircraft measured a peak 700 mb flight-level wind of 116 kt in the northeastern eyewall and a dropsonde measured a minimum pressure of 954 mb. These data support an initial intensity of 105 kt.

Environmental conditions are expected to remain favorable for some additional strengthening during the next day or two. The uw-cimms objective secondary eyewall formation technique continues to predict a high chance of an eyewall replacement during the next day or so. In fact…a recent trmm microwave pass showed some evidence of a secondary eyewall. These eyewall cycles can produce hard to predict fluctuations in intensity. For now…the new intensity forecast call for some additional strengthening followed by a leveling off of the intensity. In 3-4 days….increasing southwesterly shear and cooler ssts should induce gradual weakening…although Irene is expected to remain a large and powerful hurricane…or even grow in size…as it nears New England.

The hurricane has been moving northwestward or 310/10 kt. Irene is expected to turn toward the north-northwest then north through a break in the subtropical ridge over the western atlantic during the next couple of days. After that time…the hurricane is forecast to turn north-northeastward around the northwestern side of the ridge. Between 72 and 96 hours…there remains uncertainty as to whether Irene turns back toward the north ahead of a mid-latitude trough moving into the great lakes region at that time. The new ECMWF shows much more amplification of the trough… Which has resulted in its track shifting over 100 miles to the west…and this skillful long-range model now defines the western edge of the guidance envelope. Overall…the guidance envelope has shifted a little westward at days 4 and 5. The new track forecast is close to the previous advisory and is between the GFS and ECMWF models. This is also close to the TVCA and experimental hurricane forecast improvement project…HFIP…consensus tracks.

Forecast positions and max winds

Init 24/2100z 23.1n 74.7w 105 kt 120 mph
12h 25/0600z 24.3n 75.8w 110 kt 125 mph
24h 25/1800z 26.1n 76.8w 115 kt 135 mph
36h 26/0600z 28.2n 77.3w 115 kt 135 mph
48h 26/1800z 30.1n 77.3w 110 kt 125 mph
72h 27/1800z 34.3n 75.8w 100 kt 115 mph
96h 28/1800z 39.5n 73.0w  85 kt 100 mph
120h 29/1800z 47.0n 69.0w  55 kt 65 mph…post-trop/extratrop

Coastal Watches/Warnings and 3-Day Forecast Cone for Storm Center

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[Image of 3-day forecast and coastal areas under a warning or a watch]
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About this product:

This graphic shows an approximate representation of coastal areas under a hurricane warning (red), hurricane watch (pink), tropical storm warning (blue) and tropical storm watch (yellow). The orange circle indicates the current position of the center of the tropical cyclone. The black line, when selected, and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical. If only an L is displayed, then the system is forecast to be a remnant low. The letter inside the dot indicates the NHC’s forecast intensity for that time:

D: Tropical Depression – wind speed less than 39 MPH
S: Tropical Storm – wind speed between 39 MPH and 73 MPH
H: Hurricane – wind speed between 74 MPH and 110 MPH
M: Major Hurricane – wind speed greater than 110 MPH

NHC tropical cyclone forecast tracks can be in error. This forecast uncertainty is conveyed by the track forecast "cone", the solid white and stippled white areas in the graphic. The solid white area depicts the track forecast uncertainty for days 1-3 of the forecast, while the stippled area depicts the uncertainty on days 4-5. Historical data indicate that the entire 5-day path of the center of the tropical cyclone will remain within the cone about 60-70% of the time. To form the cone, a set of imaginary circles are placed along the forecast track at the 12, 24, 36, 48, 72, 96, and 120 h positions, where the size of each circle is set so that it encloses 67% of the previous five years official forecast errors. The cone is then formed by smoothly connecting the area swept out by the set of circles.

There is also uncertainty in the NHC intensity forecasts. The Maximum 1-minute Wind Speed Probability Table provides intensity forecast and uncertainty information.

It is also important to realize that a tropical cyclone is not a point. Their effects can span many hundreds of miles from the center. The area experiencing hurricane force (one-minute average wind speeds of at least 74 mph) and tropical storm force (one-minute average wind speeds of 39-73 mph) winds can extend well beyond the white areas shown enclosing the most likely track area of the center. The distribution of hurricane and tropical storm force winds in this tropical cyclone can be seen in the Wind History graphic linked above.

Considering the combined forecast uncertainties in track, intensity, and size, the chances that any particular location will experience winds of 34 kt (tropical storm force), 50 kt, or 64 kt (hurricane force) from this tropical cyclone are presented in tabular form for selected locations and forecast positions. This information is also presented in graphical form for the 34 kt, 50 kt, and 64 kt thresholds.