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Hurricane Maria Forecast Discussion Number 42

2017-09-26 16:41:40| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Sep 26 2017 000 WTNT45 KNHC 261441 TCDAT5 Hurricane Maria Discussion Number 42 NWS National Hurricane Center Miami FL AL152017 1100 AM EDT Tue Sep 26 2017 The satellite presentation of Maria has continued to slowly degrade over the past 24 hours, as deep convection is now confined to the southeastern portion of the circulation. Peak surface wind estimates from the Stepped Frequency Microwave Radiometer on the reconnaissance aircraft have been around 60 kt both overnight and this morning, but due to sampling considerations for such a large wind field the initial wind speed is held at 65 kt for this advisory. Cool waters and moderate west-northwesterly shear are expected to cause a gradual decrease in intensity over the next couple of days, and Maria is forecast to weaken to a tropical storm later today or tonight. Little change in strength is expected later in the period while Maria accelerates east-northeastward and begins to interact with a frontal boundary over the north Atlantic. Maria continues to move slowly northward around the western side of a subtropical ridge. A mid- to upper-level ridge over the northeastern United States to the north of Maria is likely to keep the cyclone's forward motion slow for the next 24-36 h. After that time, a mid-latitude trough moving across the Great Lakes region is expected to lift Maria east-northeastward or northeastward at an increasing forward speed. The track guidance remains in good agreement on the scenario but there continue to be large speed differences after 48 hours. The new official forecast is a little slower than the previous one at days 3-5 to be more in line with the various consensus aids. KEY MESSAGES: 1. Maria is forecast to continue moving northward, paralleling the U.S. east coast for the next 36 hours, and will likely bring some direct impacts to portions of the North Carolina coast through Wednesday where a tropical storm warning is in effect. 2. Storm surge flooding, especially along the sound side of the North Carolina Outer Banks, is expected, and a storm surge warning and watch are in effect for portions of eastern North Carolina. 3. Swells generated by Maria are affecting much of the east coast of the United States. These swells are also affecting Bermuda, the Turks and Caicos Islands, and the Bahamas. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office for more information. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 33.6N 73.1W 65 KT 75 MPH 12H 27/0000Z 34.3N 73.1W 60 KT 70 MPH 24H 27/1200Z 35.1N 73.0W 60 KT 70 MPH 36H 28/0000Z 35.7N 72.4W 55 KT 65 MPH 48H 28/1200Z 36.1N 70.9W 55 KT 65 MPH 72H 29/1200Z 37.6N 63.6W 55 KT 65 MPH 96H 30/1200Z 42.5N 49.5W 55 KT 65 MPH 120H 01/1200Z 50.5N 30.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Hurricane Lee Forecast Discussion Number 34

2017-09-26 16:39:02| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 26 2017 000 WTNT44 KNHC 261438 TCDAT4 Hurricane Lee Discussion Number 34 NWS National Hurricane Center Miami FL AL142017 1100 AM AST Tue Sep 26 2017 Lee is small but impressive hurricane this morning with a well-defined eye on visible satellite images. Satellite intensity estimates are a little higher and support an initial wind speed of at least 90 kt. Further strengthening is possible for the next day or so while Lee continues moving over warm waters with relatively light shear. Most of the guidance shows Lee getting a bit stronger, and the cyclone stands some chance of becoming a major hurricane within the next 24 hours or so. The official forecast is raised from the previous one, and is on the high side of the guidance. Weakening should begin on Thursday as shear increases and water temperatures decrease. The small tropical cyclone should weaken fairly quickly at higher latitudes and become absorbed in a large extratropical low over the northeastern Atlantic Ocean. Lee continues moving westward at 9 kt. The hurricane should gradually turn to the northwest on Wednesday and to the north on Thursday as it moves around a ridge over the east-central Atlantic. Thereafter, Lee is likely to accelerate to the northeast as it enters the faster mid-latitude flow. There are some speed differences in the models but overall not a lot of cross-track spread. The new forecast is faster than the previous one, in the direction of the latest HFIP corrected-consensus model. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 29.9N 53.7W 90 KT 105 MPH 12H 27/0000Z 30.0N 55.1W 95 KT 110 MPH 24H 27/1200Z 30.6N 56.2W 95 KT 110 MPH 36H 28/0000Z 31.7N 56.8W 90 KT 105 MPH 48H 28/1200Z 33.3N 56.7W 85 KT 100 MPH 72H 29/1200Z 39.0N 51.5W 70 KT 80 MPH 96H 30/1200Z 46.0N 35.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 01/1200Z...DISSIPATED $$ Forecaster Blake

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Hurricane Maria Forecast Discussion Number 41

2017-09-26 10:47:02| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Tue Sep 26 2017 000 WTNT45 KNHC 260846 TCDAT5 Hurricane Maria Discussion Number 41 NWS National Hurricane Center Miami FL AL152017 500 AM EDT Tue Sep 26 2017 Maria is feeling the effects of the cool sea surface temperatures left in the wake of Hurricane Jose. Satellite imagery shows that the convective pattern is gradually losing organization, with the remaining convection in a cluster to the southeast of the center and in bands well to the east of the center. In addition, the aircraft-reported central pressure has risen to 970 mb. While there have been no observations of hurricane-force winds from the Stepped Frequency Microwave Radiometer on the NOAA Hurricane Hunter currently in the cyclone, it is likely that they still exist in areas east of the center where the airplane has not yet sampled. The initial intensity is lowered to a somewhat uncertain 65 kt based mainly on the rising central pressure since the last advisory. The combination of the cool water and moderate shear should cause Maria to gradually weaken during the forecast period, with the system now expected to weaken to a tropical storm in less than 24 h. Near the 120 h point, the cyclone is expected to merge with a frontal system and become extratropical. The new intensity forecast is an update of the previous advisory. The initial motion remains 360/6, with Maria moving northward on the western side of the subtropical ridge. A mid- to upper-level ridge over the northeastern United States to the north of the cyclone is likely to keep the motion slow for the next 36-48 h. After that, the mid-latitude westerlies are forecast to move southward across the northeastern United States and break down the subtropical ridge. This should lead to Maria turning east-northeastward and accelerating after 48 h. The track guidance is in good agreement with this scenario, and the new forecast track is close to the previous track until 120 h, where it is nudged a bit to the south. The track is also close to the center of the guidance envelope. KEY MESSAGES: 1. Maria is forecast to continue moving northward, paralleling the U.S. east coast for the next 36-48 hours, and it is likely that some direct impacts will occur along portions of the North Carolina coast beginning later today, where a Tropical Storm Warning is in effect. 2. Storm surge flooding, especially along the sound side of the North Carolina Outer Banks, is expected beginning later today, and a Storm Surge Watch has been issued for portions of eastern North Carolina. 3. Swells generated by Maria are affecting much of the east coast of the United States from Florida through southern New England. These swells are also affecting Bermuda, Puerto Rico, the northern coast of Hispaniola, the Turks and Caicos Islands, and the Bahamas. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office for more information. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 32.9N 73.1W 65 KT 75 MPH 12H 26/1800Z 33.7N 73.2W 65 KT 75 MPH 24H 27/0600Z 34.6N 73.1W 60 KT 70 MPH 36H 27/1800Z 35.4N 72.7W 60 KT 70 MPH 48H 28/0600Z 35.8N 71.7W 55 KT 65 MPH 72H 29/0600Z 37.0N 66.0W 55 KT 65 MPH 96H 30/0600Z 41.0N 53.0W 55 KT 65 MPH 120H 01/0600Z 48.0N 35.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Hurricane Lee Forecast Discussion Number 33

2017-09-26 10:45:31| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Sep 26 2017 000 WTNT44 KNHC 260845 TCDAT4 Hurricane Lee Discussion Number 33 NWS National Hurricane Center Miami FL AL142017 500 AM AST Tue Sep 26 2017 Lee's cloud pattern has continued to become better organized this evening. The eye has cleared out and has warmed to nearly 10 degrees Celsius, and the eye wall cloud tops have cooled to -63 degrees Celsius. The initial intensity is increased modestly to 85 kt and is based on a blend of the subjective and objective Dvorak T-numbers. It is worth noting that the ADT adjusted raw T-number yields an estimated intensity of 97 kt based on an eye scene-type. The previously noted southeasterly shear undercutting the diffluent flow aloft has certainly diminished and should remain low for the next 48 hours or so. During this initial period, Lee could get a little stronger as indicated in the HWRF hurricane model and the Decay-SHIPS. Afterward, increasing vertical shear, primarily due to the outflow generated by Maria, and decreasing sea surface temperatures should induce a gradual weakening trend as the cyclone moves into a high latitude baroclinic zone and ultimately becomes an extratropical cyclone in 4 days. The intensity forecast is basically an update of 6 hours ago, and follows an average of the IVCN and Florida State Superensemble guidance. The initial motion is estimated to be westward, or 260/9 kt. The cyclone is expected to continue moving within the easterly mid-level steering flow, produced by a relatively narrow mid-tropospheric ridge situated to the north, during the next 24 hours. Afterward, a combination of a broad mid- to upper-level shortwave trough moving out of the eastern Canadian Provinces and a subtropical ridge building east of Lee should steer the hurricane gradually northwestward and northward. On day 3 and beyond, Lee is forecast to accelerate northeastward as it becomes embedded in a deep-layer high latitude southwesterly flow downstream from the aforementioned shortwave trough. Global models and the Cyclone Phase Evolution analysis/forecast product show Lee become a extratropical cyclone no later than day 4. The NHC forecast track is a little south of the previous one through 48 hours, but similar thereafter, and is based on the TVCX and HCCA consensus models. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 30.0N 52.5W 85 KT 100 MPH 12H 26/1800Z 29.9N 53.9W 90 KT 105 MPH 24H 27/0600Z 30.2N 55.4W 90 KT 105 MPH 36H 27/1800Z 30.9N 56.4W 90 KT 105 MPH 48H 28/0600Z 32.2N 56.6W 85 KT 100 MPH 72H 29/0600Z 36.9N 53.0W 75 KT 85 MPH 96H 30/0600Z 44.5N 40.2W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 01/0600Z 50.9N 22.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts

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Hurricane Maria Forecast Discussion Number 40

2017-09-26 04:43:38| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Mon Sep 25 2017 000 WTNT45 KNHC 260243 TCDAT5 Hurricane Maria Discussion Number 40 NWS National Hurricane Center Miami FL AL152017 1100 PM EDT Mon Sep 25 2017 Maria's deep convection continues to slowly diminish, especially over the western semicircle of the circulation, where only a few cold tops are seen. The Air Force Hurricane Hunters reported an SFMR-observed surface wind of 67 kt over the northeast quadrant, so the current intensity is maintained at 70 kt for the time being. Although vertical shear is not forecast by the dynamical guidance to increase significantly over the next few days, cooler waters and drier air are likely to cause Maria to weaken to a tropical storm by late Tuesday or Wednesday. By the end of the forecast period, global models indicate that the system will have transformed into a frontal cyclone over the northern Atlantic, and this is also reflected in the official forecast. Maria continues to move northward quite slowly, or 360/6 kt, on the western side of a subtropical high pressure area. A mid-level ridge over the northeastern United States should continue to retard the system's forward progress for another day or two. Afterward, this ridge is predicted to weaken, and Maria should begin to accelerate northeastward to east-northeastward away from the United States east coast, ahead of a broad mid-tropospheric trough. The official track forecast is very similar to the previous one and is in line with the multi-model consensus. This is also between the faster GFS and slower ECMWF tracks. KEY MESSAGES: 1. Maria is forecast to continue moving northward, paralleling the U.S. east coast, and it is likely that some direct impacts will occur along portions of the North Carolina coast beginning Tuesday, where a Tropical Storm Warning is in effect. 2. Storm surge flooding, especially along the sound side of the North Carolina Outer Banks, is expected beginning on Tuesday, and a Storm Surge Watch has been issued for portions of eastern North Carolina. 3. Swells generated by Maria are affecting much of the east coast of the United States from Florida through southern New England. These swells are also affecting Bermuda, Puerto Rico, the northern coast of Hispaniola, the Turks and Caicos Islands, and the Bahamas. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office for more information. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 32.3N 73.1W 70 KT 80 MPH 12H 26/1200Z 33.2N 73.2W 65 KT 75 MPH 24H 27/0000Z 34.1N 73.2W 65 KT 75 MPH 36H 27/1200Z 35.0N 73.0W 60 KT 70 MPH 48H 28/0000Z 35.5N 72.4W 60 KT 70 MPH 72H 29/0000Z 36.5N 68.4W 60 KT 70 MPH 96H 30/0000Z 40.0N 57.5W 60 KT 70 MPH 120H 01/0000Z 47.0N 40.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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