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Tropical Depression KARL Forecast Discussion Number 29

2016-09-21 16:49:08| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED SEP 21 2016 000 WTNT42 KNHC 211443 TCDAT2 TROPICAL DEPRESSION KARL DISCUSSION NUMBER 29 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM AST WED SEP 21 2016 A research flight by the NOAA P3 aircraft earlier this morning had a difficult time closing off a well-defined center of circulation. However, we are able to track what looks like a reasonable center on early-morning visible satellite imagery. Based on the latest satellite images and the P3 data, it does appear that the center has wobbled toward the northwest and slowed down a bit. However, the longer-term 12-hour motion estimate is still west-northwestward, or 295/8 kt. Most of the deep convection remains displaced well to the east of the center, but new convection has recently been developing just to the north and northwest. The initial intensity is held at 30 kt based on earlier reports from the NOAA P3 and a 1254 UTC ASCAT-B scatterometer pass. Karl remains located to the south and southwest of a mid-level high. However, the depression is expected to turn northwestward later today when it begins to move between the high and a mid- to upper-level low located near the Carolina coast. Karl should then turn northward and then accelerate toward the northeast from 48 hours and beyond once it becomes embedded in the mid-latitude westerlies. The track guidance remains in generally good agreement on this scenario, and the main differences appear toward the end of the forecast period when the ECMWF remains much slower than the other models. The new official forecast remains very close to a consensus of the GFS and ECMWF models, which did not require any significant changes from the previous advisory. The distance between Karl and the upper-level low that has been adversely affecting it during the past couple of days appears to be increasing a bit, and the shear vector over the cyclone has become south-southeasterly. Although the global models continue to indicate that the shear will decrease over the next few days, they do not agree on the direction of that shear. In addition, the models do not agree on how much moisture there will be in the mid-level environment around the cyclone. As a result, the intensity forecast is complicated, and confidence is not very high. For continuity's sake, the updated intensity forecast is very similar to the previous forecast during the first 3 days, and then it is a little lower at days 4 and 5 based on the latest guidance. Karl is expected to become extratropical by day 5, which agrees with the latest guidance from the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 20.8N 57.8W 30 KT 35 MPH 12H 22/0000Z 22.1N 59.6W 30 KT 35 MPH 24H 22/1200Z 24.0N 62.0W 30 KT 35 MPH 36H 23/0000Z 25.7N 63.6W 35 KT 40 MPH 48H 23/1200Z 27.2N 64.8W 45 KT 50 MPH 72H 24/1200Z 31.0N 62.2W 60 KT 70 MPH 96H 25/1200Z 36.0N 52.5W 70 KT 80 MPH 120H 26/1200Z 44.0N 38.5W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg/Gallina/Veenhuis

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Tropical Storm LISA Forecast Discussion Number 8

2016-09-21 16:34:44| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED SEP 21 2016 000 WTNT43 KNHC 211434 TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 1100 AM AST WED SEP 21 2016 The cloud pattern of Lisa has not changed much since the previous advisory. A 0911 UTC SSMIS image suggested that the low-level center was located on the western edge of the central convection. The 12Z Dvorak Data-T numbers from SAB and TAFB decreased and a partial ASCAT-B pass from 1115 UTC only showed 30-35 kt winds in the northeastern quadrant. However, the initial intensity is held at 45 kt given the lack of clear evidence of weakening and in agreement with the the latest Dvorak CI numbers of T3.0/45 kt. There is only a small opportunity for the cyclone to strengthen before the shear increases even further in 24 to 36 hours. Weakening is expected after that time, and later in the period, as the mid-level environment becomes quite dry, the cyclone should weaken to a remnant low. The new NHC intensity forecast is similar to the previous one and is near the middle of the guidance in the first 36 hours and then is near or below the weaker LGEM solution after that time. The initial motion estimate is a somewhat uncertain 320/07, given the lack of confidence in the location of the center. Lisa will move northwestward during the next 72 hours into a weakness in the subtropical ridge over the eastern Atlantic, and then recurve into the mid-latitude westerlies on days 4 and 5. The global models are in generally good agreement on this scenario, with the ECMWF lying on the left side of the guidance cluster and the GFS shifting to the right this cycle. The new NHC track forecast is an update of the previous one but has been adjusted for the initial position and motion. This forecast is near a blend of the latest GFS and ECMWF tracks and is well to the left of the GFDL and HWRF models, which lie nearly 200 n mi east of the rest of the guidance at days 3 and 4. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 18.0N 32.5W 45 KT 50 MPH 12H 22/0000Z 18.6N 33.4W 50 KT 60 MPH 24H 22/1200Z 19.7N 34.9W 45 KT 50 MPH 36H 23/0000Z 20.9N 36.5W 45 KT 50 MPH 48H 23/1200Z 22.3N 38.0W 40 KT 45 MPH 72H 24/1200Z 25.0N 41.0W 30 KT 35 MPH 96H 25/1200Z 28.5N 43.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/1200Z 34.0N 41.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brennan

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Tropical Depression KARL Forecast Discussion Number 28

2016-09-21 10:35:15| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED SEP 21 2016 000 WTNT42 KNHC 210835 TCDAT2 TROPICAL DEPRESSION KARL DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST WED SEP 21 2016 Karl's structure is very difficult to determine this morning. Satellite data indicate that the low-level center moved westward far away from the convection, and currently it is hard to say if Karl possess a closed circulation or not. Assuming that it still does, the maximum winds are estimated generously at 30 kt, since the cloud pattern has become less organized. I would not be surprised if early visible satellite images will reveal that the cyclone has degenerated into a broad area of low pressure. Global models have totally failed so far in forecasting the upper-level winds surrounding Karl. The upper-low near Karl which unanimously all models have been forecasting to weaken is still strong and producing shear over the cyclone. Given such a resilient shear pattern, additional weakening is anticipated today. However, most of the models are still predicting a favorable pattern for intensification, and on this basis as well as continuity, the NHC forecast calls for some strengthening beyond 36 hours while Karl moves away from the hostile tropics. By the end of the forecast period, Karl should be rapidly losing tropical characteristics while it interacts with the mid-latitude flow. The initial motion is also highly uncertain, giving that we have been following the low-cloud swirl defining the alleged center. The best estimate is toward the west or 280 degrees at 12 kt. Karl is approaching the southwestern edge of the subtropical ridge, and this pattern should result in a turn to the northwest and then north during the following two days. After that time, a sharp recurvature is anticipated around the northwestern portion of the subtropical high and ahead of a mid-latitude shortwave. This sharp recurvature is the solution provided by most of the track models, and the NHC forecast is in the middle if the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 20.2N 57.6W 30 KT 35 MPH 12H 21/1800Z 20.9N 59.3W 25 KT 30 MPH 24H 22/0600Z 23.0N 61.5W 30 KT 35 MPH 36H 22/1800Z 25.0N 64.0W 35 KT 40 MPH 48H 23/0600Z 27.0N 65.5W 45 KT 50 MPH 72H 24/0600Z 30.0N 64.0W 60 KT 70 MPH 96H 25/0600Z 35.5N 56.5W 75 KT 85 MPH 120H 26/0600Z 43.0N 42.0W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Avila

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Tropical Storm LISA Forecast Discussion Number 7

2016-09-21 10:33:19| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED SEP 21 2016 000 WTNT43 KNHC 210833 TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 500 AM AST WED SEP 21 2016 Lisa's cloud pattern has gradually become better organized into a comma-like shape, although the system still appears to be somewhat elongated from southwest to northeast. Upper-level outflow remains weak over the southeastern quadrant of the circulation. Dvorak classifications from both TAFB and SAB yield an intensity estimate of 45 kt, and that value is used for the advisory. The storm has less than 24 hours before west-southwesterly shear associated with an upper-level trough near 40W-50W longitude becomes prohibitively large for strengthening. Therefore, some slight additional intensification could occur today, but beyond 24 hours Lisa is forecast to steadily weaken. By days 4-5, although the shear is predicted to weaken when Lisa moves under the trough axis, the cyclone should have been disrupted too much by the earlier hostile environment to make a recovery. The official forecast is close to the LGEM guidance through 48 hours and a little below that model thereafter. The center is not easy to locate and the initial motion is a rather uncertain 315/8 kt, which is partially based on continuity from earlier estimates. A weak mid-tropospheric ridge to the north and northeast of Lisa should maintain a generally northwestward motion through 72 hours or so. Later in the forecast period, an approaching trough in the westerlies, which is also expected to accelerate Karl to the northeast, should cause Lisa to turn northward over the eastern Atlantic. The official track forecast is similar to the previous one and is close to a consensus of the ECMWF, GFS, and UKMET global models. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 17.5N 32.2W 45 KT 50 MPH 12H 21/1800Z 18.2N 33.2W 50 KT 60 MPH 24H 22/0600Z 19.1N 34.5W 50 KT 60 MPH 36H 22/1800Z 20.1N 35.9W 45 KT 50 MPH 48H 23/0600Z 21.3N 37.4W 40 KT 45 MPH 72H 24/0600Z 24.1N 40.4W 30 KT 35 MPH 96H 25/0600Z 27.5N 43.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/0600Z 32.5N 43.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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Tropical Storm LISA Forecast Discussion Number 6

2016-09-21 04:41:08| National Hurricane Center (Atlantic)

Issued at 1100 PM AST TUE SEP 20 2016 000 WTNT43 KNHC 210241 TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 1100 PM AST TUE SEP 20 2016 Deep convection has increased in coverage near and to the northeast of the center of Lisa this evening. Although the exact center has been difficult to pinpoint in infrared satellite images, it appears that it is located near the southwestern edge of the convection due to some southwesterly shear. Satellite intensity estimates still support a wind speed of around 40 kt, so the initial intensity is unchanged for this advisory. Lisa has about 24 hours over warm water and in a marginally conducive upper-level wind environment in which to strengthen. After that time, an upper-level low to Lisa's northwest is expected to produce strong southwesterly shear over the cyclone, which should cause weakening. As a result, the NHC intensity forecast calls for peak intensity in about 24 hours, followed by steady weakening thereafter. The official forecast is near the upper-end of the guidance at 24 hours, but is slightly lower than the consensus after that time. The somewhat uncertain initial motion estimate is 315/9 kt. The track forecast appears to be fairly straight forward as Lisa should continue moving northwestward during the next several days toward a break in the subtropical ridge. Late in the forecast period, the cyclone should turn northward ahead of a deepening mid- to upper-level trough over the west-central Atlantic. The dynamical models are in good agreement on this scenario, and the NHC forecast is near a blend of the typically better performing ECMWF and GFS models. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 17.1N 31.7W 40 KT 45 MPH 12H 21/1200Z 17.8N 32.7W 45 KT 50 MPH 24H 22/0000Z 18.6N 34.0W 50 KT 60 MPH 36H 22/1200Z 19.4N 35.2W 45 KT 50 MPH 48H 23/0000Z 20.6N 36.7W 40 KT 45 MPH 72H 24/0000Z 23.6N 39.8W 30 KT 35 MPH 96H 25/0000Z 26.5N 42.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/0000Z 31.0N 43.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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