Hurricane Irene Intermediate Advisory From the National Hurricane Center Miami, Florida, August 26, 2011 (8 AM EDT)

Miami, Florida—(ENEWSPF)—August 26, 2011 – UPDATE 8 AM EDT eNews Park Forest continues to post raw data regarding hurricane Irene to keep the public informed as quickly as possible.


Reports from an air force reserve hurricane hunter aircraft indicate that the intensity of Irene is not quite at major hurricane status. The maximum flight-level winds at 700 mb were 109 kt about 75 n mi east-northeast of the center…and the maximum surface winds reported from the stepped frequency microwave radiometer were 87 kt. Based on these data…the intensity estimate is reduced to 95 kt…which is also between the satellite intensity estimates of 102 kt from TAFB and 90 kt from sab. The aircraft data indicate that a 20 n mi wide eye is present and that the central pressure remains near 942 mb.

The initial motion is now 360/12. Irene is moving through a weakness at the western end of the subtropical ridge…and it should recurve into the westerlies during the forecast period. The track guidance is tightly clustered around a northward motion during the first 24 hr…followed by a turn toward the north-northeast. The new forecast track calls for Irene to make landfall along the north Carolina outer banks in about 36 hr…then pass near the coast of the Mid-Atlantic states before making landfall in New England in Roughly 60 hours. There has been no significant change in the track guidance since the last advisory… And while the forecast track Has been adjusted slightly to the east this should be considered a noise-level change. After landfall… Irene should merge with the Core of the westerlies and turn northeastward with acceleration.

Water vapor imagery and analsyes from CIMSS at the university of Wisconsin suggest that Irene is encountering light to moderate southwesterly vertical wind shear.  This…along with the current cyclone structure and dry air advecting toward the hurricane in water vapor imagery…argue against significant strengthening…. and indeed the intensity guidance shows little change in strength before landfall.  On the other hand…the eyewall convection is currently strong…and the sea surface temperatures along the forecast track are 28-29c.  This suggests some modest strengthening is possible.  Irene is expected to be near the category 2/3 boundary when it reaches the vicinity of the outer banks…and slowly weaken after that. After moving into New England…Irene should weaken quickly as it undergoes extratropical transition.

Irene remains a very large tropical cyclone.  The wind radii have been adjusted based on aircraft data and an ASCAT overpass.


INIT 26/0900Z 29.3N 77.2W 95 KT 110 MPH
12H 26/1800Z 31.0N 77.2W 100 KT 115 MPH
24H 27/0600Z 33.1N 76.9W 100 KT 115 MPH
36H 27/1800Z 35.3N 76.1W 105 KT 120 MPH
48H 28/0600Z 37.8N 75.0W 85 KT 100 MPH
72H 29/0600Z 45.0N 70.4W 55 KT 65 MPH…INLAND
96H 30/0600Z 53.0N 61.0W 40 KT 45 MPH…POST-TROP/EXTRATROP
120H 31/0600Z 58.5N 44.0W 40 KT 45 MPH…POST-TROP/EXTRATROP

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

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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.