TR Forecast #3 for TS Isaac - TR eats crow in 12 hr

[Coredesat]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org. For official information, please refer to NHC and NWS products.

...Tropical Depression 9 over the central Atlantic...should not threaten land...

The estimated position of Tropical Depression 9 at midnight EDT was 27.5°N 53.5°W. Poor confidence in position due to poor organization of convection and the secondary blob of convection to the southeast of the main circulation center.

Estimated maximum sustained winds are 35 mph. The estimated minimum central pressure is 1012 mbar. The system appears to be moving northwestward at 12 mph.

Little change in strength is expected in the next 24 hours due to marginally unfavorable upper-level shear and dry air impinging on the system from the west. The depression could still become a tropical storm by this time tomorrow.

Steering currents favor a continued northwestward motion for at least the next 24 hours before a frontal trough turns it northward, then northeastward after that. This trough should initiate extratropical transition after 48 hours as it accelerates the system over colder waters and increases the shear over it. The forecast track is a bit to the west of the NHC 11 PM track, closer to the GFDL but not as far west as the BAM shallow guidance.

On this forecast track, the depression should not threaten land as a tropical system.



Next forecast will be posted tomorrow at midnight.

[Coredesat]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org. For official information, please refer to NHC and NWS products.

...Tropical Storm Isaac not expected to threaten land as a tropical system...

The estimated position of Tropical Storm Isaac at 11:30 PM EDT was 29.0°N 55.5°W. Fair confidence in this position based on the IR and vapor satellite loops.

Estimated maximum sustained winds are 40 mph. The estimated minimum central pressure is 1007 mbar. The system appears to be moving west-northwestward at 9 mph.

Any strengthening should be slow and rather minor due to continued unfavorable conditions in the area. Dry air has also worked its way into Isaac's circulation, and is currently inhibiting any significant strengthening or organization.

The model guidance shifted a little to the left, and the NHC remained on the right side of the model plot at the 11 PM advisory. This forecast is slightly to the left of the NHC's to take the GFDL into account. This forecast strengthens Isaac only slightly before a trough coming off the east coast of the US initiates extratropical transition in 72 hours or so. This trough should sweep Isaac out to sea, but extratropical Isaac may affect parts of Newfoundland with gale or storm force winds early next week.

Forecast Positions and Max Winds

Initial: 29.0°N 55.5°W - 35 kt
12 hr: 30.0°N 57.0°W - 40 kt
24 hr: 31.0°N 58.6°W - 40 kt
36 hr: 32.5°N 59.9°W - 45 kt
48 hr: 34.6°N 60.2°W - 45 kt
72 hr: 38.0°N 59.5°W - 50 kt extratropical cyclone
96 hr: extratropical cyclone

[Evil Jeremy]

WNW?

[Coredesat]

Isaac appears to be moving west-northwest or west on the satellite loops. I don't expect that to last very long.

[rainstorm]

looks wnw to me

[Coredesat]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org. For official information, please refer to NHC and NWS products.

...Isaac could become a hurricane...

Welcome to the "I eat crow" edition of the forecast. I didn't expect Isaac to strengthen much if at all, and look what it does.

The estimated position of Tropical Storm Isaac at midnight EDT was 30.2°N 57.6°W. Good confidence in this position based on the IR and vapor satellite loops.

Estimated maximum sustained winds are 70 mph. The estimated minimum central pressure is 996 mbar. The system appears to be moving west-northwestward at 10 mph.

I have underestimated Isaac's tenacity, as it has somehow managed to strengthen despite a great deal of dry air in the area. This forecast calls for minimal hurricane strength, but should Isaac become a hurricane, it won't be one for very long. Weakening is likely after 24 hours as the frontal trough off the eastern U.S. coast approaches.

This forecast is very slightly to the west of the NHC official forecast, and more along the lines of the model guidance. The front coming off the east coast of the US should turn Isaac to the north within 24 hours, then initiate extratropical transition in 48-72 hours, and the persistent dry air and increasing shear should weaken Isaac below hurricane strength (should it get there) after 24 hours. There is still a chance that extratropical Isaac could affect areas of southeastern Newfoundland with gale force winds near the end of the forecast period, as the front sweeps it northeastward.

Forecast Positions and Max Winds

Initial: 30.2°N 57.6°W - 60 kt
12 hr: 31.7°N 59.1°W - 65 kt
24 hr: 33.2°N 60.4°W - 65 kt
36 hr: 35.2°N 61.6°W - 55 kt
48 hr: 37.4°N 62.0°W - 50 kt becoming extratropical
72 hr: 41.5°N 61.0°W - 45 kt extratropical cyclone
96 hr: 47.0°N 54.0°W - 45 kt extratropical cyclone