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Tropical Storm Karen Forecast Discussion Number 18
2019-09-26 16:53:44| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Sep 26 2019 000 WTNT42 KNHC 261453 TCDAT2 Tropical Storm Karen Discussion Number 18 NWS National Hurricane Center Miami FL AL122019 1100 AM AST Thu Sep 26 2019 Karen has been maintaining a cluster of convection to the west of its center, but visible satellite images and wind data from NOAA buoy 40149 to the northeast suggest that the low-level circulation is becoming elongated. This structure has been confirmed by a late-arriving ASCAT pass, and that data also show that Karen is producing winds to 40 kt within the deep convection. Karen is embedded in the flow between a mid-level high centered over the central Atlantic and a mid- to upper-level low which is slowly retrograding westward over the Bahamas. This is maintaining a north-northeastward motion of 015/12 kt. The central Atlantic high is expected to weaken over the next 2 days, while a new high develops over the western Atlantic, causing Karen to make a clockwise loop well to the southeast of Bermuda. Once the western Atlantic high becomes established, Karen is then expected to move generally westward on days 3 through 5. There have been no significant changes among the track models, and the new NHC track forecast is therefore very similar to the previous one. Relatively light winds aloft and warm ocean waters could allow Karen to maintain its intensity for another day or two. After that time, however, an increase in northerly shear will likely allow ambient dry air to infiltrate into the circulation further. The dynamical models--which we're now heavily favoring in our forecasts--are showing gradual weakening and even a loss of organized deep convection in a few days. Therefore, Karen is now forecast to degenerate into a remnant low by day 3. The low is expected to plow into strong southwesterly shear on days 4 and 5 while it moves westward over the southwestern Atlantic, which should keep it as a remnant low or possibly cause it to open up into a trough of low pressure. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 26.6N 63.3W 40 KT 45 MPH 12H 27/0000Z 27.6N 62.5W 40 KT 45 MPH 24H 27/1200Z 28.1N 61.1W 35 KT 40 MPH 36H 28/0000Z 28.0N 60.4W 35 KT 40 MPH 48H 28/1200Z 27.8N 60.6W 30 KT 35 MPH 72H 29/1200Z 27.3N 63.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/1200Z 27.1N 66.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/1200Z 27.0N 69.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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Hurricane Lorenzo Forecast Discussion Number 16
2019-09-26 16:53:44| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Sep 26 2019 000 WTNT43 KNHC 261453 TCDAT3 Hurricane Lorenzo Discussion Number 16 NWS National Hurricane Center Miami FL AL132019 1100 AM AST Thu Sep 26 2019 A review of microwave satellite imagery from last night suggests that Lorenzo underwent an eyewall replacement cycle, with the outer eyewall becoming predominant around 06Z-09Z. Around that time, the hurricane started to rapidly intensify, with the eye becoming much better defined in conventional satellite imagery. Raw Data-T numbers from both subjective and objective versions of the Dvorak Technique suggest that the maximum winds have increased to near 115 kt, which will be the initial intensity for this advisory. The initial wind radii have been revised based on a recently received scatterometer overpass. The initial motion is 295/11. Lorenzo is approaching a developing break in the subtropical ridge caused by a series of mid-latitude troughs to the northwest of the hurricane, and the track guidance models are in excellent agreement that Lorenzo should recurve through the break during the forecast period. There are no significant changes to the guidance since the last advisory, and there are no significant changes to the forecast track either. Data from the SHIPS model suggest that Lorenzo will be in an area of maximum potential intensities of 125-135 kt for the next 3-4 days. This suggests that the rapid intensification should end in the next 6-12 h as the actual intensity approaches those speeds. Fluctuations in strength due to eyewall replacement cycles are expected during the 12-36 h period. The global models suggest that Lorenzo will subsequently interact with an upper-level trough during recurvature, which should cause a period of increased shear and some weakening of the cyclone around 48 h. By 120 h, the hurricane should weaken due to movement over colder water and into strong shear in the mid-latitude westerlies. While its exact ranking will be determined later, Lorenzo is one of the largest and most powerful hurricanes of record for the central tropical Atlantic, with the only comparable hurricane in recent times near there being Gabrielle of 1989. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 15.4N 40.2W 115 KT 130 MPH 12H 27/0000Z 16.7N 41.4W 125 KT 145 MPH 24H 27/1200Z 18.5N 42.6W 125 KT 145 MPH 36H 28/0000Z 20.2N 43.5W 120 KT 140 MPH 48H 28/1200Z 21.9N 43.9W 110 KT 125 MPH 72H 29/1200Z 25.2N 43.3W 100 KT 115 MPH 96H 30/1200Z 29.0N 41.0W 100 KT 115 MPH 120H 01/1200Z 34.0N 37.0W 90 KT 105 MPH $$ Forecaster Beven
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Hurricane Lorenzo Forecast Discussion Number 15
2019-09-26 12:03:48| National Hurricane Center (Atlantic)
Issued at 600 AM AST Thu Sep 26 2019 000 WTNT43 KNHC 261003 TCDAT3 Hurricane Lorenzo Special Discussion Number 15 NWS National Hurricane Center Miami FL AL132019 600 AM AST Thu Sep 26 2019 Shortly after the issuance of the 0900 UTC advisory, Lorenzo's eye quickly and drastically became more apparent in conventional satellite imagery. The slightly ragged but clearing eye of the hurricane is surrounded by very cold cloud tops, and it has become clear that Lorenzo is rapidly intensifying. A 0900 UTC TAFB Dvorak classification of 6.0/6.0 (115 kt) was used as the primary basis for increasing the intensity of Lorenzo. Because objective fixes from just a few hours ago were much lower, the intensity of the hurricane has been increased, perhaps conservatively, to 110 kt. Since this is 10 kt above the previous 12-h forecast, a special advisory is required to update the intensity forecast. Additional strengthening is possible later today. Earlier intensity guidance indicated that Lorenzo's intensity should level off in a day or so, though none of the guidance correctly anticipated the rate at which the hurricane has strengthened this morning. Now that the hurricane has a closed eyewall, fluctuations in intensity due to eyewall replacement cycles are also possible, though this is not explicitly reflected in the updated forecast. By the end of the forecast period, the updated NHC forecast is relaxed to the original forecast and shows some gradual weakening. Further adjustments, especially at 72 h and beyond, may be required later this morning. No changes were made to the track forecast, which is based on the previous regular advisory. FORECAST POSITIONS AND MAX WINDS INIT 26/1000Z 15.2N 39.3W 110 KT 125 MPH 12H 26/1800Z 16.0N 40.6W 120 KT 140 MPH 24H 27/0600Z 17.7N 41.9W 120 KT 140 MPH 36H 27/1800Z 19.5N 43.0W 115 KT 130 MPH 48H 28/0600Z 21.2N 43.8W 110 KT 125 MPH 72H 29/0600Z 24.6N 43.5W 100 KT 115 MPH 96H 30/0600Z 28.0N 42.0W 100 KT 115 MPH 120H 01/0600Z 33.0N 38.0W 95 KT 110 MPH $$ Forecaster Zelinsky
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Tropical Storm Karen Forecast Discussion Number 17
2019-09-26 10:34:06| National Hurricane Center (Atlantic)
Issued at 500 AM AST Thu Sep 26 2019 000 WTNT42 KNHC 260834 TCDAT2 Tropical Storm Karen Discussion Number 17 NWS National Hurricane Center Miami FL AL122019 500 AM AST Thu Sep 26 2019 Karen is barely a tropical storm. A pair of ASCAT passes from several hours ago showed maximum winds between 30 and 35 kt in the southeastern quadrant of the storm. Those passes also indicate that the circulation is quite broad and weak on the west side. Based on the ASCAT data and the TAFB Dvorak classification, the initial wind speed is held at 35 kt. The storm appears quite disheveled in satellite images, with an elongated east to west convective pattern and a lack of well-defined banding features. Karen has not been able to take advantage of the relatively favorable environment that it has been in during the past day or so, which was well anticipated by the dynamical models, but poorly forecast by the statistical-dynamical aids. The storm will remain in generally favorable conditions through tonight, so it should be able to maintain its intensity or perhaps strengthen slightly during that time. After that, however, the models show a steady increase in shear and drier air in the vicinity of the cyclone. These conditions should cause weakening and will likely lead to the system either losing its deep convection and becoming a remnant low or dissipating entirely in 3 or 4 days when it moves into a region of strong westerly shear. The NHC intensity forecast is the same as the previous one and leans more on the GFS and ECMWF guidance. The tropical storm is still moving north-northeastward at 13 kt steered by the flow between a mid-level ridge to its east and a mid- to upper-level low to its west over the Bahamas. The low is expected to weaken and lift out during the next few days allowing a low- to mid-level ridge to strengthen and build to the north of Karen. This change in the steering flow should cause Karen, or its remnants, to move slower to the northeast and east through Friday, followed by a motion to the west-southwest this weekend. Only minor changes were made to the previous NHC track forecast, and this one lies closest to the HCCA model. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 25.5N 63.5W 35 KT 40 MPH 12H 26/1800Z 27.0N 62.9W 35 KT 40 MPH 24H 27/0600Z 27.9N 61.5W 35 KT 40 MPH 36H 27/1800Z 28.0N 60.3W 35 KT 40 MPH 48H 28/0600Z 27.9N 60.1W 35 KT 40 MPH 72H 29/0600Z 27.3N 62.5W 30 KT 35 MPH 96H 30/0600Z 27.0N 65.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/0600Z 26.8N 67.4W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi
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Hurricane Lorenzo Forecast Discussion Number 13
2019-09-26 04:36:03| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 25 2019 000 WTNT43 KNHC 260235 TCDAT3 Hurricane Lorenzo Discussion Number 13 NWS National Hurricane Center Miami FL AL132019 1100 PM AST Wed Sep 25 2019 A small eye has been intermittently appearing in infrared satellite imagery over the past few hours, and a recent WINDSAT microwave overpass showed that the inner-core of Lorenzo is trying to consolidate. There is still some dry air wrapping in toward the center of circulation as seen in an SSMIS overpass at 2020 UTC. This could be the reason why the hurricane has not been able to develop a well-defined eye as of yet. An ASCAT-B scatterometer pass this evening showed a still expanding wind field associated with Lorenzo, and the 50-kt winds now extend up to 90 n mi from the center in the northern semicircle. A blend of the subjective intensity estimates from TAFB and SAB support the initial intensity of 85 kt for this advisory. Based on the improving inner-core structure, large central dense overcast, and an expanding cirrus shield around the hurricane, it is believed that the dry air that has been entrained near the center will mix out soon. This should allow for the eyewall to completely develop and Lorenzo should reach major hurricane intensity within the next 24 hours. Lorenzo will continue over warm waters and in a light shear environment during the next couple of days, which should allow for some additional strengthening. By 72 hours, increasing shear due to west to southwest winds aloft ahead of an approaching mid-latitude trough should begin to weaken the hurricane. The official intensity forecast is very near the previous one, and is on the high end of the guidance through 72 hours. Lorenzo is moving west-northwest at 13 kt to the south of a mid-level ridge. The model guidance is in very good agreement on a break developing in the ridge between 45W-50W in the next couple of days, which should result in a turn to the northwest. From day 3-5, the cyclone is expected to turn north then northeast around the periphery of the mid-level ridge to its east. The official forecast was nudged just a little to the right of the previous one starting at 36 h and is on the left side of tightly clustered consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 14.7N 38.1W 85 KT 100 MPH 12H 26/1200Z 15.2N 39.6W 95 KT 110 MPH 24H 27/0000Z 16.8N 41.2W 105 KT 120 MPH 36H 27/1200Z 18.5N 42.3W 110 KT 125 MPH 48H 28/0000Z 20.4N 43.3W 110 KT 125 MPH 72H 29/0000Z 23.8N 43.9W 105 KT 120 MPH 96H 30/0000Z 27.5N 42.4W 100 KT 115 MPH 120H 01/0000Z 31.9N 39.1W 95 KT 110 MPH $$ Forecaster Latto
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