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Tropical Depression JULIA Forecast Discussion Number 17

2016-09-18 04:32:48| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT SAT SEP 17 2016 000 WTNT41 KNHC 180232 TCDAT1 TROPICAL DEPRESSION JULIA DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112016 1100 PM EDT SAT SEP 17 2016 I have two options this evening. The first one, which is very attractive, is to classify Julia as a remnant low and terminate advisories. The second one is to keep Julia as a tropical depression in this advisory given that there was deep convection associated with the center only a few hours ago. Although it lacks thunderstorm activity, the convection has returned over and over again for the past day or so when we think it will not. I will then adopt the second option. Strong upper-level northerly winds are expected to continue affecting the circulation, and if the convection returns it will quickly be removed from the center. Therefore, Julia is forecast once again to become a remnant low soon and gradually decay. Julia is drifting northwestward at about 3 kt embedded within very light steering flow. Most of the global models keep a low meandering over water off the southeast U.S. coast, and so does the NHC forecast. Some global models actually regenerate the low, but given the strong shear, this solution does not seem realistic. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 30.6N 76.5W 25 KT 30 MPH 12H 18/1200Z 30.9N 76.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 19/0000Z 31.5N 77.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 19/1200Z 32.0N 77.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 20/0000Z 32.5N 77.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/0000Z...DISSIPATED $$ Forecaster Avila

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Tropical Depression SEVENTEEN-E Forecast Discussion Number 1

2016-09-18 04:31:46| Tropical Depression LIDIA

Issued at 900 PM MDT SAT SEP 17 2016

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Tropical Storm KARL Forecast Discussion Number 15

2016-09-18 04:31:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST SAT SEP 17 2016 000 WTNT42 KNHC 180231 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST SAT SEP 17 2016 Karl continues to struggle. The tropical storm is producing a few patches of deep convection to the north and east of the exposed center, but the cyclone lacks banding features. An ASCAT-B pass just prior to 0000Z captured a portion of the circulation and showed that the winds were lower there than they were in the previous pass. Based on that data and the Dvorak classifications, the initial wind speed is lowered a little to 35 kt. The poor structure of Karl is likely due to the combined effects of southwesterly shear and dry mid-level air. These unfavorable atmospheric conditions and marginally warm sea surface temperatures should keep Karl relatively steady state for the next day or so. After that time, lower shear, slightly more moisture, and warmer sea surface temperatures should allow the cyclone to strengthen. The intensity models are a bit higher this cycle at the longer range, and the NHC forecast has been nudged upward. This prediction lies near the lower end of the guidance, in best agreement with the SHIPS model. The center of Karl is moving south of due west at about 10 kt. A general westward motion at a slightly faster pace is expected during the next day or two while Karl is steered by the flow on the south side of a subtropical ridge. A turn to the west-northwest is predicted beyond a couple of days as Karl moves on the southwestern periphery of the ridge and toward a weakness. There is not a significant amount of spread in the models, or the ensemble members of the GFS and ECMWF, and the official forecast is largely an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 17.8N 41.3W 35 KT 40 MPH 12H 18/1200Z 17.9N 43.3W 35 KT 40 MPH 24H 19/0000Z 18.1N 46.0W 40 KT 45 MPH 36H 19/1200Z 18.6N 48.6W 45 KT 50 MPH 48H 20/0000Z 19.4N 51.1W 50 KT 60 MPH 72H 21/0000Z 21.2N 56.1W 55 KT 65 MPH 96H 22/0000Z 23.7N 61.4W 65 KT 75 MPH 120H 23/0000Z 25.8N 65.2W 75 KT 85 MPH $$ Forecaster Cangialosi

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Tropical Storm KARL Forecast Discussion Number 14

2016-09-17 22:34:20| National Hurricane Center (Atlantic)

Issued at 500 PM AST SAT SEP 17 2016 000 WTNT42 KNHC 172034 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 PM AST SAT SEP 17 2016 Convection continues to flare up and down near the center of Karl, with a larger mass well to the northeast of the center. In addition, the circulation looks more elongated than earlier today, perhaps due to the convective asymmetry. The initial wind speed is held at 40 kt since the system does not look all that different, although the satellite classifications are a bit lower. Karl could still weaken a little bit in the short term while the cyclone is in a recovery stage from its interaction with an upper-level low. Gradual strengthening is then forecast by early next week as the storm encounters very warm water, low shear, and a marginal moisture environment. Model guidance is very similar to the previous cycle, except for the ECMWF which shows a more powerful cyclone by day 5. Very little change was made to the official forecast, which continues to be most similar to a blend of the SHIPS/LGEM models. The initial motion estimate is unchanged from the previous one, 265/11. Karl should begin to gain some latitude by Monday as it moves around the southern side of the subtropical ridge. A west-northwestward motion is forecast to begin on Tuesday due to the orientation of the ridge, and this motion could continue for the rest of the 5-day period. The biggest change since the last cycle is that model guidance is showing a stronger ridge in the central Atlantic, which would prolong the west-northwestward motion. The track models have shifted westward at long range, and the official forecast is moved in that direction, but not as far west as the 12Z ECMWF/GFS solutions. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 18.1N 40.4W 40 KT 45 MPH 12H 18/0600Z 17.9N 42.3W 35 KT 40 MPH 24H 18/1800Z 17.8N 45.0W 40 KT 45 MPH 36H 19/0600Z 18.1N 47.6W 40 KT 45 MPH 48H 19/1800Z 18.8N 50.3W 45 KT 50 MPH 72H 20/1800Z 20.6N 55.4W 50 KT 60 MPH 96H 21/1800Z 23.0N 60.5W 60 KT 70 MPH 120H 22/1800Z 25.0N 64.5W 70 KT 80 MPH $$ Forecaster Blake

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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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