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Tropical Storm HENRI Forecast Discussion Number 10
2015-09-11 10:40:50| National Hurricane Center (Atlantic)
Issued at 500 AM AST FRI SEP 11 2015 000 WTNT43 KNHC 110840 TCDAT3 TROPICAL STORM HENRI DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082015 500 AM AST FRI SEP 11 2015 Overall, Henri's cloud pattern has become slightly better organized since the last advisory. While nearly all of the cyclone's deep convection is still located well to the northeast of the center, a relatively new convective burst over this area has grown in coverage and cloud tops have cooled. Subjective Dvorak classifications remain below tropical storm strength, but the initial intensity held at 35 kt due to the cyclone's increasing forward speed and somewhat improved satellite presentation. Southerly shear appears to be diminishing over the cyclone, as has been forecast by the large-scale models. The lower shear could allow for some additional intensification to take place during the next 12 hours or so while it remains over warm-enough waters. However, the continued presence of dry air in the near-storm environment and Henri's disorganized appearance suggest that any intensification should be negligible. After the cyclone crosses the northern wall of the Gulf Stream in less than 18 hours, substantially lower sea surface temperatures and increasingly stable air should induce weakening soon after that. A plausible alternate scenario, presented by some of the global models, is that Henri could degenerate into a trough later today. The cyclone or its remnants are forecast to undergo extratropical transition in about 36 hours, with the system likely to be absorbed by a larger extratropical cyclone by 72 hours. The new intensity forecast is very similar to the previous one. The initial motion estimate is 010/14. Henri is expected to accelerate north-northeastward and then northeastward during the next day or so as it encounters the fast-paced flow ahead of a deep longwave trough digging into eastern North America and the western Atlantic. The post-tropical cyclone or its remnants should then turn east-northeastward over the north Atlantic. The new track forecast is adjusted to the left of the previous forecast and lies on the right side of the guidance envelope. The latter part of this forecast, when the storm is expected to be post-tropical, is partially based on guidance provided by NOAA's Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 36.2N 60.3W 35 KT 40 MPH 12H 11/1800Z 39.0N 59.3W 40 KT 45 MPH 24H 12/0600Z 43.0N 56.4W 40 KT 45 MPH 36H 12/1800Z 46.5N 52.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 13/0600Z 48.9N 45.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 14/0600Z...ABSORBED $$ Forecaster Kimberlain
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