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Tropical Storm Maria Forecast Discussion Number 49

2017-09-28 10:36:24| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Thu Sep 28 2017 000 WTNT45 KNHC 280836 TCDAT5 Tropical Storm Maria Discussion Number 49 NWS National Hurricane Center Miami FL AL152017 500 AM EDT Thu Sep 28 2017 Maria's satellite presentation has not changed much during the past six hours, with 15-20 kt of northwesterly shear continuing to displace much of the deep convection to the east of the center. Despite the discrepancy between aircraft observations and Dvorak estimates noted yesterday, a pair of ASCAT passes from a few hours ago showed maximum winds in the 50-55 kt range. Even with the assumption that the resolution of the ASCAT data may not have revealed the highest winds, an analysis suggests that Maria has weakened back to a 60-kt tropical storm. Little change in intensity is anticipated during the next two days while Maria moves over sea surface temperatures of 26-27 degrees Celsius, and while vertical shear decreases during the next 24 hours. After 48 hours, a marked jump in shear and much colder waters should induce more weakening, and model guidance indicates that Maria should complete extratropical transition by day 3. The extratropical low should then be absorbed by a larger system over the northeastern Atlantic by day 4. This scenario is in agreement with guidance provided by the NOAA Ocean Prediction Center. Maria is becoming embedded in the mid-latitude westerlies and is now moving toward the east-northeast, or 060/7 kt. The cyclone is expected to turn eastward very soon, but then turn back toward the east-northeast in 36 hours as a positively tilted trough moves off the New England and Atlantic Canada coasts. The speed differences among the track models are not as significant as they were yesterday, although the updated NHC track forecast was nudged southward for much of the forecast period to follow an overall modest shift in the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 36.8N 71.0W 60 KT 70 MPH 12H 28/1800Z 36.8N 68.8W 55 KT 65 MPH 24H 29/0600Z 37.0N 64.9W 55 KT 65 MPH 36H 29/1800Z 38.0N 59.7W 55 KT 65 MPH 48H 30/0600Z 40.0N 53.1W 55 KT 65 MPH 72H 01/0600Z 46.4N 35.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 02/0600Z...DISSIPATED $$ Forecaster Berg

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Hurricane Maria Forecast Discussion Number 48

2017-09-28 04:33:18| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Wed Sep 27 2017 000 WTNT45 KNHC 280233 TCDAT5 Hurricane Maria Discussion Number 48 NWS National Hurricane Center Miami FL AL152017 1100 PM EDT Wed Sep 27 2017 Maria continues to have convective bands over the eastern and northeastern portions of its circulation, with drier air inhibiting convection over much of its western semicircle. Dvorak intensity estimates are below hurricane strength, but this has been the case for the last couple of days, where aircraft observations showed the system stronger than indicated by the satellite-based estimates. Since the cloud pattern has not deteriorated significantly from earlier today, Maria is kept as a hurricane for now. Only gradual weakening is expected since SSTs do not cool much until after 48 hours, and baroclinic processes may help maintain intensity for another day or so thereafter. Later in the forecast period, the post-tropical cyclone should become absorbed by a larger extratropical low over the far northeastern north Atlantic. The 72- and 96-hour forecast positions, intensity, and wind radii were coordinated with the NOAA Ocean Prediction Center. Maria is gradually turning to the right as it nears the mid-latitude westerlies, and the motion estimate is now 040/6 kt. Over the next few days, the cyclone should accelerate eastward to east-northeastward ahead of a broad mid-level trough moving through the northeastern United Sates and off the northeast United States coast. There continues to be significant along-track, i.e. speed, differences between the ECMWF and GFS models later in the period, and the official forecast is nearly an average of these 2 model tracks. This is also close to the latest multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 36.8N 71.5W 65 KT 75 MPH 12H 28/1200Z 36.9N 70.1W 65 KT 75 MPH 24H 29/0000Z 36.9N 67.0W 60 KT 70 MPH 36H 29/1200Z 37.4N 62.6W 55 KT 65 MPH 48H 30/0000Z 39.0N 57.0W 55 KT 65 MPH 72H 01/0000Z 44.5N 41.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 02/0000Z 51.0N 18.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 03/0000Z...ABSORBED $$ Forecaster Pasch

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Hurricane Lee Forecast Discussion Number 39

2017-09-27 22:34:16| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Sep 27 2017 000 WTNT44 KNHC 272034 TCDAT4 Hurricane Lee Discussion Number 39 NWS National Hurricane Center Miami FL AL142017 500 PM AST Wed Sep 27 2017 Lee looks like a classic major hurricane on satellite today, with a fairly clear eye and an impressive outflow pattern aloft. The most noticeable change during the day is that the eye has shrunk a little bit, perhaps suggesting Lee may undergo another eyewall cycle. Otherwise, the eye temperatures and eyewall convection are similar to 6 hours ago, resulting in similar Dvorak estimates. Thus, the wind speed will remain 100 kt for this advisory. Lee should be near its peak intensity tonight and begin to weaken tomorrow as vertical wind shear increases and SSTs cool. The system should be losing tropical characteristics by late week, and will likely transition into a post-tropical cyclone on Saturday due to it moving over very cold water. The official intensity forecast is basically an update of the previous one, near the model consensus, and shaded toward the global models, due to the interaction with the mid-latitudes. Lee has turned even farther to the right, and is now moving north-northwestward at 7 kt. The hurricane should turn northward overnight and northeastward by late Thursday as it moves around the western periphery of a subtropical ridge. Lee should accelerate rapidly northeastward on Friday due to it encountering fast mid-latitude flow. Model guidance is tightly clustered, so the official forecast is close to the previous one, on the ECMWF side of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 31.2N 57.1W 100 KT 115 MPH 12H 28/0600Z 32.2N 57.4W 95 KT 110 MPH 24H 28/1800Z 34.3N 56.6W 85 KT 100 MPH 36H 29/0600Z 37.3N 53.9W 75 KT 85 MPH 48H 29/1800Z 41.0N 48.3W 60 KT 70 MPH 72H 30/1800Z 48.5N 30.0W 50 KT 60 MPH...POST-TROPICAL 96H 01/1800Z...DISSIPATED $$ Forecaster Blake

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Hurricane Lee Forecast Discussion Number 38

2017-09-27 16:49:45| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 27 2017 000 WTNT44 KNHC 271449 TCDAT4 Hurricane Lee Discussion Number 38 NWS National Hurricane Center Miami FL AL142017 1100 AM AST Wed Sep 27 2017 After an eyewall replacement overnight, satellite images indicate that a larger clear eye has formed, with the coldest cloud-top temperatures seen to date observed with the cyclone. While subjective Dvorak estimates have been fluctuating between 90-102 kt, the latest objective estimate is 102 kt, and a 1050 UTC AMSU estimate from CIMSS is 104 kt. A blend of these data gives an initial wind speed of 100 kt, making Lee the 5th major hurricane of the 2017 Atlantic season. A gradual decrease in water temperatures should start a weakening trend within 12-24 hours, with a faster weakening forecast on Thursday and Friday as Lee enters a high-shear environment. Guidance is in good agreement on this scenario, and the latest forecast is very close to the previous one. Lee has turned northwestward, or 315/6. The hurricane should turn to the north on Thursday and northeast by Friday while it moves around the subtropical ridge. Lee is expected to move quite quickly to the northeast on Friday and Saturday as it accelerates in mid-latitude flow. No significant changes were made to the previous track, and the new forecast lies between the ECMWF and the HFIP corrected-consensus model. Around day 3, the cyclone should be close to a cold front, but most of the models still show it separate from that feature. By day 4, all of the guidance have the system decaying into a trough, and that is the solution provided below. An ASCAT pass from this morning indicated that Lee has grown in size, so the initial and forecast wind radii have been modified to reflect that change. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 30.6N 56.8W 100 KT 115 MPH 12H 28/0000Z 31.4N 57.3W 95 KT 110 MPH 24H 28/1200Z 33.0N 57.2W 90 KT 105 MPH 36H 29/0000Z 35.5N 55.5W 80 KT 90 MPH 48H 29/1200Z 39.0N 51.5W 70 KT 80 MPH 72H 30/1200Z 46.5N 34.5W 55 KT 65 MPH 96H 01/1200Z...DISSIPATED $$ Forecaster Blake

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Hurricane Maria Forecast Discussion Number 46

2017-09-27 16:49:18| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Wed Sep 27 2017 000 WTNT45 KNHC 271449 TCDAT5 Hurricane Maria Discussion Number 46 NWS National Hurricane Center Miami FL AL152017 1100 AM EDT Wed Sep 27 2017 Deep convection and banding has increased over the eastern and northeastern portion of the large circulation of Maria since yesterday. An Air Force Reserve reconnaissance aircraft has measured peak flight-level winds of 74 kt and several believable SFMR winds around 65 kt in the convection well northeast of the center this morning. Based on these data, the initial wind speed is adjusted to 65 kt, which makes Maria a hurricane once again. Although the shear is forecast to decrease over Maria during the next couple of days, cool sea surface temperatures are likely to result in a slow decrease in intensity. The new NHC intensity forecast is a little above the previous advisory due to the slightly higher initial intensity. Maria is expected to become an extratropical low over the north Atlantic by 96 h and be absorbed by a larger extratropical low over the northeastern Atlantic by day 5. Maria is finally making its much anticipated north-northeast turn, with an estimated motion of 015/5. The hurricane is expected to turn east-northeastward on Thursday as it enters the mid-latitude westerly flow. A trough moving into eastern North America late this week should cause Maria to accelerate east-northeastward over the north Atlantic on Friday and Saturday. The spread in the guidance is still largely along track after 36 hours, and the NHC forecast remains near the model consensus to account for these differences. KEY MESSAGES: 1. Maria is forecast to slowly move away from the North Carolina coast later today. However, tropical storm conditions are expected to continue along portions of the North Carolina coast through this afternoon. 2. Storm surge flooding is occurring, especially along the sound side of the North Carolina Outer Banks, 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, Atlantic Canada, Bermuda, the Bahamas, and the Turks and Caicos Islands. 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 27/1500Z 35.6N 72.6W 65 KT 75 MPH 12H 28/0000Z 36.1N 72.1W 65 KT 75 MPH 24H 28/1200Z 36.5N 70.5W 60 KT 70 MPH 36H 29/0000Z 36.7N 67.3W 55 KT 65 MPH 48H 29/1200Z 37.7N 62.4W 55 KT 65 MPH 72H 30/1200Z 42.5N 47.5W 50 KT 60 MPH 96H 01/1200Z 50.0N 26.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 02/1200Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ Forecaster Brown

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