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Tropical Storm KARL Forecast Discussion Number 13
2016-09-17 16:52:48| National Hurricane Center (Atlantic)
Issued at 1100 AM AST SAT SEP 17 2016 000 WTNT42 KNHC 171452 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST SAT SEP 17 2016 Karl has been in a fairly steady state during the past day or more with convection periodically firing near the center and a larger area of more continuous thunderstorms far from the center. Ship BATFR18 reported sustained winds of about 40 kt at 1100 UTC, which support keeping that wind speed for this advisory. The shear that has been affecting Karl should gradually diminish over the next couple of days as it moves away from a nearby upper-level low. A small amount of weakening is possible in the short term since the system is still struggling against the shear. Thereafter, strengthening is anticipated due to Karl likely moving over very warm waters concurrent with rather light shear. One question mark is the amount of available moisture in the mid-levels, with both the ECMWF and the GFS showing a somewhat dry environment. While a lot of the tropical-cyclone-specific intensity guidance shows a hurricane at long range, the marginal moisture environment forecast by those two global models makes me think twice about going too high. The new forecast is very similar to the previous one and is similar to a blend of the SHIPS/LGEM models. Karl has been wobbling a little south of due west during the day, depending on how much convection is near the center. A strengthening low- to mid-level ridge over the central Atlantic is expected to continue pushing Karl south of due west during the next 24 hours. After that time, Karl should move more to the west-northwest around the weakening ridge through day 4, well to the northeast of the Leeward Islands, and possibly turn northwestward by 120 hours while the cyclone approaches a weakness in the ridge. The spread in the models have increased since the last advisory, perhaps due to Karl's interaction with the upper-low. The new model consensus and the previous official forecast were very close to one another, so no significant changes are made in the new NHC forecast. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 18.3N 39.0W 40 KT 45 MPH 12H 18/0000Z 18.1N 40.9W 35 KT 40 MPH 24H 18/1200Z 17.8N 43.6W 35 KT 40 MPH 36H 19/0000Z 17.8N 46.2W 40 KT 45 MPH 48H 19/1200Z 18.3N 48.7W 45 KT 50 MPH 72H 20/1200Z 20.2N 54.0W 50 KT 60 MPH 96H 21/1200Z 22.5N 59.0W 60 KT 70 MPH 120H 22/1200Z 25.0N 63.0W 70 KT 80 MPH $$ Forecaster Blake
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