Hurricane Irene Intermediate Advisory From the National Hurricane Center Miami, Florida, August 26, 2011 (5 PM EDT)

Miami, Florida—(ENEWSPF)—August 26, 2011 – UPDATE 5 PM EDT eNews Park Forest continues to post raw data regarding hurricane Irene to keep the public informed as quickly as possible.


The aircraft did not find any higher winds after the release of the previous advisory. In fact…data from near the conclusion of the flight support a slight lower initial intensity. The aircraft did report hurricane-force winds at flight level and SFMR winds of 50-55 kt 135 n mi east of the center…showing the large size of the wind field. Buoy observations and data from an earlier ASCAT pass show that the tropical-storm-force winds extend outward about 225-250 n mi over the eastern semicircle. Recent microwave data and observations from the aircraft indicate that the inner core has eroded. Although Irene will be moving over warm water during the next 12-18 hours…the lack of an inner core will likely preclude any restrengthening. Although not shown in the official forecast…Irene could weaken just below hurricane strength before reaching southern New England. However…impacts from this large tropical cyclone will not be very different if it is a strong tropical storm or low-end hurricane. Irene has the potential to produce damaging winds…storm surge flooding…and extremely heavy rains almost anywhere from eastern North Carolina northward through New England. 

Irene is still moving northward or 360/12 kt. Irene is expected to turn north-northeastward tonight and continue on that heading up the east coast…and be moving at about 15-17 kt as it approaches Long Island…much slower than normal for storms in this area…which will produce extended periods of tropical storm and hurricane-force winds in many areas. The models have been very consistent on the future track of Irene over the last several cycles. The new track forecast is very similar to the previous advisory and lies between the GFS and ECMWF.


INIT  26/2100Z 31.7N  77.4W   85 KT 100 MPH  12H  27/0600Z 33.4N  77.1W   80 KT  90 MPH  24H  27/1800Z 35.5N  76.3W   75 KT  85 MPH...INLAND  36H  28/0600Z 38.2N  75.0W   70 KT  80 MPH...OVER WATER  48H  28/1800Z 41.8N  73.0W   60 KT  70 MPH...INLAND  72H  29/1800Z 50.5N  65.0W   45 KT  50 MPH...POST-TROP/EXTRATROP  96H  30/1800Z 56.5N  51.0W   40 KT  45 MPH...POST-TROP/EXTRATROP 120H  31/1800Z 58.0N  32.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

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

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Other images: 3-Day track on5-Day track on5-Day track off
[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.


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