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Tropical Storm Maria Forecast Discussion Number 45

2017-09-27 10:36:17| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Wed Sep 27 2017 000 WTNT45 KNHC 270836 TCDAT5 Tropical Storm Maria Discussion Number 45 NWS National Hurricane Center Miami FL AL152017 500 AM EDT Wed Sep 27 2017 Maria has changed little in structure since the last advisory. A band of deep convection attempted to wrap around the western side of the circulation, but that has since dissipated due to continued shear and dry air. The initial intensity remains 60 kt based on surface winds measured by the SFMR on the previous reconnaissance flight. Maria will likely be moving over some warm and cold eddies associated with the Gulf Stream during the next 2 to 3 days, and with vertical shear expected to gradually decrease during that time, only slow weakening is anticipated. After day 3, vertical shear increases significantly, and Maria is expected to complete extratropical transition by day 4. The global models then indicate that the low will be absorbed by a larger extratropical low over the northeastern Atlantic by day 5. Earlier reconnaissance fixes indicated that Maria's center was jumping around a bit, but its average motion is estimated to be slowly northward, or 005 degrees at 4 kt. Maria is moving around the western periphery of a mid-level ridge located over the central Atlantic, and it should enter the mid-latitude westerlies in about 36 hours, at which point it is expected to accelerate northeastward across the north Atlantic. Most of the model spread continues to be in the along-track direction, highlighted by the faster GFS and HWRF models and the slower ECMWF model. As was the case before, the updated NHC track forecast splits the difference between these scenarios and remains close to the multi-model consensus aids. KEY MESSAGES: 1. Maria is forecast to slowly move away from the U.S. east coast during the next day or so. However, tropical storm conditions are expected to continue along portions of the North Carolina coast through much of today. 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, 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 27/0900Z 35.1N 72.9W 60 KT 70 MPH 12H 27/1800Z 35.7N 72.7W 55 KT 65 MPH 24H 28/0600Z 36.2N 71.7W 55 KT 65 MPH 36H 28/1800Z 36.5N 69.3W 50 KT 60 MPH 48H 29/0600Z 37.0N 65.3W 50 KT 60 MPH 72H 30/0600Z 40.5N 52.5W 50 KT 60 MPH 96H 01/0600Z 47.5N 32.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 02/0600Z...ABSORBED BY A LARGER EXTRATROPICAL LOW $$ Forecaster Berg

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Hurricane Lee Forecast Discussion Number 37

2017-09-27 10:35:46| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 27 2017 000 WTNT44 KNHC 270835 TCDAT4 Hurricane Lee Discussion Number 37 NWS National Hurricane Center Miami FL AL142017 500 AM AST Wed Sep 27 2017 Conventional satellite imagery indicates that Lee has been undergoing some cloud structural changes during the past several hours. The eye has nearly doubled in size to 30 miles in diameter, the central pressure indicated in the CIMSS Objective Dvorak technique has increased a few millibars, and an earlier 2147 UTC WindSAT overpass revealed a developing outer ring surrounding the partially opened inner core. These aforementioned cloud pattern alterations arguably point to an undergoing eyewall replacement cycle, and the possibility of intensification in the short term. The initial intensity of 95 kt remains above the subjective T-numbers, and is close to the CIMSS ADT estimated intensity. The official intensity forecast reflects the possibility of Lee becoming a major hurricane later today before a weakening trend commences by early Wednesday. The global models and the FSU Cyclone Phase Evolution product agree that Lee will maintain tropical characteristics through day 3. Afterward, the guidance shows the cyclone quickly absorbed by an existing larger baroclinic system. The initial motion is estimated to be west-northwestward, or 285/8 kt. Lee should turn gradually northwestward later today, and generally northward on Thursday as the cyclone is steered by the southwestern peripheral flow of a subtropical ridge over the east-central Atlantic. Through the remaining portion of the forecast, Lee is forecast to accelerate northeastward within the strong mid-latitude southwesterly flow and ultimately dissipate in 72 hours. The model guidance suite continues to trend toward the west through the 36-hour period, and the official forecast follows suit. Beyond that time frame, the forecast is a little faster than the previous advisory and is nudged toward the HFIP Corrected Consensus technique model. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 30.2N 56.3W 95 KT 110 MPH 12H 27/1800Z 30.8N 57.0W 95 KT 110 MPH 24H 28/0600Z 32.1N 57.3W 90 KT 105 MPH 36H 28/1800Z 34.5N 56.5W 85 KT 100 MPH 48H 29/0600Z 37.8N 53.1W 75 KT 85 MPH 72H 30/0600Z 46.3N 39.0W 60 KT 70 MPH 96H 01/0600Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm Maria Forecast Discussion Number 44

2017-09-27 04:33:44| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Tue Sep 26 2017 000 WTNT45 KNHC 270233 TCDAT5 Tropical Storm Maria Discussion Number 44 NWS National Hurricane Center Miami FL AL152017 1100 PM EDT Tue Sep 26 2017 Practically all of the deep convection associated with Maria is over the eastern semicircle of the circulation, and the center is exposed near the edge of the dense overcast due to moderate west-northwesterly shear. SFMR-observed surface winds from an Air Force Hurricane Hunter aircraft support a current intensity of 60 kt, although satellite classifications indicate a much weaker cyclone. Since SSTs are not expected to cool significantly along the projected path of Maria over the next couple of days, only slight weakening is forecast up to 72 hours. Later in the forecast period, the global models depict the cyclone as embedded in a frontal zone, so the system is forecast to become extratropical by day 4. Maria continues to move slowly northward along the western periphery of a subtropical ridge. In 24-48 hours, the mid-latitude westerlies should shift southward in association with a broad mid-tropospheric trough moving across eastern North America. This should cause Maria to turn east-northeastward and then accelerate ahead of the trough by late in the week. The track models are in general agreement on this scenario, however, the guidance has become less tightly clustered. This is especially true later in the forecast period, where the ECMWF is much slower than the GFS and HWRF models. The official track forecast lies between these options and is a little to the left of the previous one in the early part of the period, in deference to the ECMWF solution. KEY MESSAGES: 1. Maria is forecast to move roughly parallel to the U.S. east coast for the next day or so, bringing 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 27/0300Z 34.9N 72.9W 60 KT 70 MPH 12H 27/1200Z 35.4N 72.8W 60 KT 70 MPH 24H 28/0000Z 36.1N 72.2W 55 KT 65 MPH 36H 28/1200Z 36.5N 70.7W 55 KT 65 MPH 48H 29/0000Z 36.8N 68.0W 55 KT 65 MPH 72H 30/0000Z 39.5N 57.5W 55 KT 65 MPH 96H 01/0000Z 46.0N 39.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 02/0000Z 53.0N 17.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Tropical Storm Maria Forecast Discussion Number 43

2017-09-26 22:33:43| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Tue Sep 26 2017 000 WTNT45 KNHC 262033 TCDAT5 Tropical Storm Maria Discussion Number 43 NWS National Hurricane Center Miami FL AL152017 500 PM EDT Tue Sep 26 2017 There has been little change to Maria's cloud pattern since the previous advisory. The center of the large circulation is located near the northwestern edge of the deep convection due to west-northwesterly shear and dry air intrusion. Reconnaissance aircraft have not found any SFMR winds higher than 60 kt for quite some time, so the initial intensity has been reduced to that value. Cool waters and moderate shear should cause some additional decrease in wind speed over the next day or so, but little change in strength is forecast later in the period as Maria accelerates east-northeastward over the north Atlantic. Maria should complete extratropical transition in about 96 hours, and could merge with a large extratropical low in about 5 days. Maria is continuing its slow northward motion around the western side of a subtropical ridge. The mid-latitude westerlies are forecast to dip southward as a large trough moves across eastern North America later this week. This should cause Maria to turn east-northeastward by Thursday, and then accelerate ahead of the trough by late in the week. The track guidance has trended slightly slower and the NHC forecast has been adjusted accordingly. The new official forecast is near the middle of the tightly clustered guidance. 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 26/2100Z 34.1N 73.0W 60 KT 70 MPH 12H 27/0600Z 34.8N 73.0W 60 KT 70 MPH 24H 27/1800Z 35.5N 72.7W 55 KT 65 MPH 36H 28/0600Z 36.0N 71.9W 55 KT 65 MPH 48H 28/1800Z 36.3N 69.9W 55 KT 65 MPH 72H 29/1800Z 38.3N 60.6W 55 KT 65 MPH 96H 30/1800Z 44.0N 44.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 01/1800Z 51.5N 25.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Hurricane Lee Forecast Discussion Number 35

2017-09-26 22:31:52| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 26 2017 000 WTNT44 KNHC 262031 TCDAT4 Hurricane Lee Discussion Number 35 NWS National Hurricane Center Miami FL AL142017 500 PM AST Tue Sep 26 2017 Satellite images indicate that the cloud-top temperatures in the eyewall of Lee have cooled this afternoon, with about the same warm temperatures in the eye. This indicates Lee remains on a strengthening trend, and the initial wind speed is set to 95 kt, near the CIMSS Advanced Dvorak Technique figure. Lee has about 24 hours to intensify before shear increases and water temperatures begin to cool. Most of the guidance now show Lee becoming a major hurricane, and the official forecast follows suit. A more significant weakening is expected by the end of the week as the hurricane moves over much colder waters and into higher shear. Model guidance is virtually unanimous on this scenario, and only minor changes were made to the previous forecast. The small tropical cyclone should become absorbed in a large extratropical low over the northeastern Atlantic Ocean within 4 or 5 days. Lee is moving westward at 8 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. The most significant change to the previous forecast is that the model guidance has trended westward with the first part of the forecast, closest to the 00 UTC ECMWF solution. Since the 12 UTC ECMWF is very consistent with its previous forecast, the NHC track forecast is adjusted westward near the point of recurvature, then is blended back with the previous forecast closer to the corrected consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 29.9N 54.6W 95 KT 110 MPH 12H 27/0600Z 30.0N 55.9W 100 KT 115 MPH 24H 27/1800Z 31.0N 56.9W 95 KT 110 MPH 36H 28/0600Z 32.4N 57.3W 90 KT 105 MPH 48H 28/1800Z 34.5N 56.7W 85 KT 100 MPH 72H 29/1800Z 41.0N 48.0W 65 KT 75 MPH 96H 30/1800Z 48.5N 30.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 01/1800Z...DISSIPATED $$ Forecaster Blake

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