...Isaac becomes extratropical as it approaches Newfoundland...

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Visible and microwave imagery indicates that Isaac has become an extratropical cyclone. Based on high resolution QuikSCAT, initial intensity is 60kts. Heavy rain and high winds can be expected over southeastern Newfoundland today.

INIT 46.0N 53.0W 50KTS...EXTRATROPICAL

This is the final forecast that will be issued by Nencweather.com on Isaac. Refer to the final forecast and advisory at 5PM from the National Hurricane Center for further updates on this system.

Powell

...Isaac starting to weaken as it moves toward Newfoundland...

Although these forecasts appear statistically reliable, always First consult and consider official products released by the National Hurricane Center. This forecast is not associated with any other professional or non-professional source of information except nencweather.com

Visible imagery indicates that the eye of Isaac has closed up. The cloud pattern of the hurricane is becoming a little elongated and banding is not as well defined. The southwestern quadrant of the cyclone does not have as impressive outflow as before. SSD T-numbers are 4.0/4.5, so I compromise intensity initially at 70kts. Southwesterly flow over Isaac is increasing, and vertical shear has increased to around 20kts, and will continue to increase as a front boundary to the west of the hurricane continues plowing eastward. Isaac is moving quickly to the north ahead of the front and will turn to the northeast by the end of the day. The cyclone should be absorbed by the frontal boundary in two to three days, and Isaac should become extratropical in 36 hours. Weakening is forecasted until then, but baroclinic interaction will maintain a fairly strong cyclone over the North Atlantic. The track is a little faster than the previous to accommodate for current motion and a little to the right with a shift in global guidance. This takes the center farther away from the Canadian maritimes, but as Isaac becomes extratropical, the wind field will expand.

INIT 34.8N 60.3W 70KTS
12HR 37.6N 59.6W 65KTS
24HR 42.4N 57.3W 65KTS
36HR 47.3N 51.7W 60KTS...EXTRATROPICAL

Powell

...Isaac reaches hurricane strength...

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Isaac has continued to become better organized under a favorable upper level regime. Mid-to-upper tropospheric temperatures are lower than normal, vertical shear is less than 10kts, and a favorable light southwesterly flow is aiding outflow. Isaac has become a Category 1 hurricane, and initial intensity is set at 65kts. High resolution QuikSCAT suggests that Isaac is approaching 65kts. The presentation of the ragged eye feature has improved this morning, along with expanded outflow. It is quite likely that Isaac will strengthen further over the next 24 hours as these favorable conditions continue. Vertical shear will begin to increase at about that time as very strong flow ahead of a trough moves eastward and captures Isaac. Given the recent intensification trend, I will bring Isaac up to 80kts in 24 hours. The time of extratropical transition is not affected however, and Isaac is still expected to become an extratropcial cyclone in about 48 hours now--albeit a more powerful one than previously anticipated. Isaac could affect the Canadian maritimes, particularly southeastern Newfoundland, in about three days. Global model guidance remains fairly clustered and the track is near the latest CONU, or basically an extension of the previous forecast.

INIT 31.3N 59.1W 65KTS
12HR 32.2N 60.0W 75KTS
24HR 34.0N 60.6W 80KTS
36HR 37.7N 60.2W 75KTS
48HR 43.0N 58.0W 65KTS...EXTRATROPICAL

Powell

...Isaac becoming a little better organized...

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Isaac has a better organized tropical storm today. The inner core has become more compact, and convection is present in all quadrants. The center of circulation is in the form of an eye, indicating some subtropical nature, but QuikSCAT indicates that the wind field is shrinking. Based on SSD estimates and QuikSCAT, initial intensity is 40kts. Vertical shear is low, and only light upper level flow is present over the storm. Some intensification as a tropical cyclone is forecasted over the next two days as Isaac moves slowly to the northwest. Shear will increase ahead of a very powerful trough to the west in about 36 hours, and Isaac will turn to the north. Intensity is leveled off after 36 hours as shear increases; however, baroclinic interaction is likely, so I do allow for a little intensification as the storm becomes extratropical. This is a little less aggressive than SHIPS. The track forecast is the near the latest CONU and moves Isaac around north Atlantic ridging, accelerating northeastward ahead of an incoming trough.

INIT 29.5N 56.5W 40KTS
12HR 29.9N 57.6W 45KTS
24HR 30.4N 58.8W 45KTS
36HR 31.8N 59.9W 50KTS
48HR 34.5N 60.6W 50KTS
72HR 42.0N 58.0W 55KTS...EXTRATROPICAL

Powell

...Isaac, the ninth named storm of the year, is harmless to land...

Although these forecasts appear statistically reliable, always First consult and consider official products released by the National Hurricane Center. This forecast is not associated with any other professional or non-professional source of information except nencweather.com

SSD T-numbers are up to 2.5, corresponding to 35kts, and QuikSCAT supports at least this intensity, so initial intensity is 35kts. Vertical shear is light, and the storm is experiencing southwest flow over the ill-organized center. The low-level circulation is rather large, but it is closed off--just not with much convection near the center. In fact, the storm has little deep convection associated with it. Based on QuikSCAT, winds seems to baroclinically extend from the center, and the storm has a large wind field. Additionally and quite unusual, an upper level low is nearly overtop of the storm, so I conclude that Isaac is not fully tropical. Recent microwave images are not available from SSMI or AMSR, so based on the low-level circulation, I will initialize as a tropical cyclone instead of a subtropical storm. Isaac will have a favorable upper level environment to work with over the next couple of days, particularly if it remains somewhat subtropical. The intensity forecast is above SHIPS and allows for a moderate tropical storm in a couple of days. Isaac should become extratropical by 96 hours as it moves northeastward over higher latitudes.

Global track guidance is actually fairly divergent. GFS shows a very shallow system, which would result in a slow moving cyclone. Indeed, this is forecasted over the next couple of days; however, it is expected that the storm will become better vertically stacked within a couple of days, and that it will become embedded in southwesterly flow ahead of very strong troughing in the western Atlantic, currently located over east CONUS. Once ridging erodes, Isaac will turn northward and quickly accelerate northeastward. As such, there is very little chance that a nearly stationary solution offered by GFS or UKMET will verify. The forecast is a concensus of GFDL and NOGAPS and is close to the latest CONU.

INIT 28.4N 55.0W 35KTS
12HR 29.1N 55.9W 35KTS
24HR 29.9N 56.9W 40KTS
36HR 31.1N 58.0W 45KTS
48HR 32.3N 59.1W 50KTS
72HR 35.5N 60.5W 50KTS
96HR 42.5N 57.0W 50KTS...EXTRATROPICAL

Powell

...Another tropical depression forms in the middle of nowhere...

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A northwestward moving tropical wave has gained enough organization to be classified as a tropical depression. QuikSCAT shows some rain-contaminated 40kt to 50kt wind vectors, but the circulation is not well defined. Objective estimates are at 30kts, and this is the initial intensity. The depression is currently experiencing southwesterly shear and the center is mostly to the south and west of convection, and banding is not very well organized. Still, vertical shear is low, and the depression has some opportunity to strengthen. SHIPS brings the system to near 50kts in 72 hours. GFS seems a bit weak, as it has been for several storms this year, and its track are slow and on the left side of guidance. The track is close to GFDL, and close to the intensity of both SHIPS and GFDL. Since the storm has not compacted a very organized center, it is not anticipated that the low pressure system will significantly benefit from baroclinic interaction in about 72 hours as it moves into higher latitudes. The track forecast anticipates steady motion, followed by increasing forward speed and a turn northward in about 48 hours as a trough approaches.

INIT 27.4N 54.1W 30KTS
12HR 28.4N 55.2W 30KTS
24HR 29.9N 56.8W 35KTS
36HR 31.8N 57.9W 40KTS
48HR 33.7N 58.3W 45KTS
72HR 37.5N 58.0W 50KTS
96HR 42.0N 53.0W 50KTS...EXTRATROPICAL

Powell