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Tropical Depression Lee Forecast Discussion Number 18

2017-09-22 22:37:57| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 22 2017 000 WTNT44 KNHC 222037 TCDAT4 Tropical Depression Lee Discussion Number 18 NWS National Hurricane Center Miami FL AL142017 500 PM AST Fri Sep 22 2017 The mid-level circulation from Lee separated from the low-level center two days ago and moved northward around the eastern periphery of a large upper-level trough. A large convective burst over the mid-level center yesterday then caused a new low-level center to develop while it moved on the northern side of the upper trough. ASCAT and ship data indicate that the small circulation is now well defined, and since deep convection has persisted near the center, advisories on Lee are being restarted. The initial wind speed is 30 kt, which could be conservative given the healthy structure seen on the last-light visible and recent microwave data. Cold upper-level temperatures from the upper trough should mitigate the effect of marginally warm waters for the next few days while Lee remains in a low-shear environment. The depression is expected to strengthen over the next few days until westerly shear is forecast to increase. The official forecast is similar to the model guidance, although it shows an earlier peak more coincident with the lower-shear, warmer-water environment. This wind speed forecast is difficult because Lee is a very small tropical cyclone, which notoriously have rapid changes, both up and down, in intensity. Lee is moving northward at about 6 kt. The depression should turn to the northeast and east over the next couple of days while it moves around a ridge over the tropical central Atlantic. Lee is forecast to become trapped beneath a mid-latitude ridge in a few days, which should cause the cyclone to drift at long range. It should be noted that models have a rather weak representation of Lee at the present time, which causes this to be an uncertain forecast. For now, the forecast is closest to the ECMWF, which has the most coherent cyclone to follow. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 30.8N 48.9W 30 KT 35 MPH 12H 23/0600Z 31.7N 48.7W 40 KT 45 MPH 24H 23/1800Z 32.3N 48.2W 45 KT 50 MPH 36H 24/0600Z 32.3N 47.2W 50 KT 60 MPH 48H 24/1800Z 32.1N 45.8W 55 KT 65 MPH 72H 25/1800Z 31.4N 43.2W 60 KT 70 MPH 96H 26/1800Z 30.5N 42.0W 55 KT 65 MPH 120H 27/1800Z 29.5N 43.0W 50 KT 60 MPH $$ Forecaster Blake

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Post-Tropical Cyclone Jose Forecast Discussion Number 69

2017-09-22 16:42:38| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 22 2017 000 WTNT42 KNHC 221442 TCDAT2 Post-Tropical Cyclone Jose Discussion Number 69 NWS National Hurricane Center Miami FL AL122017 1100 AM AST Fri Sep 22 2017 The large circulation of Jose has not changed much during the past several hours, with a small burst of moderate-to-deep convection rotating around the center. Satellite classifications support reducing the winds to 40 kt for this advisory. Surface observations are still showing sustained tropical-storm-force winds in the warning areas, so advisories will be maintained on Jose. These winds should diminish this afternoon or evening according to all of the model guidance as Jose gradually weakens. The intensity forecast is a little lower than the previous one, showing a slow decay of the winds over cold waters, which is well supported by the latest global model guidance. Jose has been erratically moving during the past 24 hours, with a southwestward drift most recently noted. The system is expected to stay trapped in light steering flow and move little for the next couple of days, then take a more westward turn by day 3 as the circulation of Maria and a ridge over the northeastern United States steer the weak cyclone. However, all models suggest it will be quite weak by day 3 and open up into a trough on day 4. Only small changes were made to the previous forecast. KEY MESSAGES: 1. Tropical-storm-force winds, especially in gusts, are occuring over portions of extreme southeastern New England. These conditions are expected to continue through this afternoon. 2. Minor coastal flooding is possible along portions of the coast of southern New England during the next few days. Please see products issued by local National Weather Service forecast offices. 3. Swells generated by Jose are affecting Bermuda and much of the U.S. east coast, and will likely cause dangerous surf and rip current conditions for the next couple of days in these areas. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 39.5N 69.4W 40 KT 45 MPH...POST-TROPICAL 12H 23/0000Z 39.4N 69.5W 35 KT 40 MPH...POST-TROPICAL 24H 23/1200Z 39.3N 69.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 24/0000Z 38.9N 68.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 24/1200Z 38.8N 68.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/1200Z 38.5N 69.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/1200Z...DISSIPATED $$ Forecaster Blake

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Hurricane Maria Forecast Discussion Number 26

2017-09-22 16:36:40| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Fri Sep 22 2017 000 WTNT45 KNHC 221436 TCDAT5 Hurricane Maria Discussion Number 26 NWS National Hurricane Center Miami FL AL152017 1100 AM EDT Fri Sep 22 2017 Even though Maria's eye has become cloud filled since the previous advisory, reconnaissance data indicate that the hurricane has not weakened. The highest flight-level wind measured by the plane was 121 kt, accompanied by SFMR winds as high as 109 kt, so the initial intensity will remain 110 kt. Microwave data and reports from the plane indicate that the eye has opened up on the southwest/west side, which is likely an indicator of increasing southwesterly shear. This shear is expected to persist for at least the next 36 hours, but Maria will be moving over 28-29 degree Celsius water during that time. Therefore, only a very gradual reduction in wind speed is expected for the next 2 days. After that time, Maria will begin to move over a cold pool left behind by Jose, where sea surface temperatures are 26 degrees Celsius or colder. Additional weakening is therefore anticipated on days 3 through 5, and the NHC intensity forecast is a little lower than SHIPS, LGEM, and the intensity consensus to account for the possible effect of the colder waters. Maria continues to move northwestward, or 325/7 kt, around the southwestern periphery of a mid-level high centered south of Bermuda. The hurricane should turn north-northwestward later today and then northward in 24-36 hours when it begins to move between the high and an elongated trough extending southwest of Jose. Although a general northward motion is expected through the end of the forecast period, some notable speed differences develop among the track models from day 3 and beyond. The ECMWF and UKMET are the main outliers, lying on the western side of the guidance envelope. To account for those possible solutions, the NHC track forecast leans a little left of the TVCN multi-model consensus toward the end of the forecast period. KEY MESSAGES: 1. Flash flooding continues in portions of Puerto Rico and the Dominican Republic due to persistent heavy rainfall from Maria's trailing rainbands. Continue to follow advice from local officials to avoid these life-threatening flooding conditions. 2. Swells from Maria are beginning to reach the coast of the southeastern United States and will last for several days. These swells are likely to cause dangerous surf and life-threatening rip currents along the coast for the next several days, even with Maria forecast to remain well offshore over the western Atlantic Ocean. 3. Maria will be closer to the east coast of the United States and Bermuda by the middle of next week, but it is too soon to determine what, if any, direct impacts there might be in these areas. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 22.3N 71.0W 110 KT 125 MPH 12H 23/0000Z 23.5N 71.5W 105 KT 120 MPH 24H 23/1200Z 25.0N 72.0W 100 KT 115 MPH 36H 24/0000Z 26.5N 72.3W 100 KT 115 MPH 48H 24/1200Z 27.9N 72.3W 95 KT 110 MPH 72H 25/1200Z 30.0N 71.6W 85 KT 100 MPH 96H 26/1200Z 32.0N 71.0W 75 KT 85 MPH 120H 27/1200Z 34.0N 71.0W 65 KT 75 MPH $$ Forecaster Berg

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Hurricane Maria Forecast Discussion Number 25

2017-09-22 10:44:40| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Fri Sep 22 2017 000 WTNT45 KNHC 220844 TCDAT5 Hurricane Maria Discussion Number 25 NWS National Hurricane Center Miami FL AL152017 500 AM EDT Fri Sep 22 2017 Reports from an Air Force Reserve Hurricane Hunter aircraft near 0500 UTC indicated that the central pressure of Maria had risen to 959 mb, accompanied by flight-level winds and SFMR surface wind estimates that supported an intensity near 110 kt. Since that time, the cloud tops in the eyewall have cooled, but the eye has become less distinct in conventional satellite imagery. The initial intensity is held at 110 kt pending the arrival of the next plane near 1200 UTC, but it is possible this is a little generous. Maria is starting to be affected by 15-20 kt of southwesterly vertical wind shear, with the first sign of this being a decrease in convective banding in the western semicircle. The large-scale models forecast some shear to persist through the forecast period, and as a result the intensity guidance predicts a gradual weakening. In addition, after 48 h the forecast track takes the center of Maria over waters that were cooled significantly by the passage of former Hurricane Jose. Based on these factors, the new intensity forecast calls for a slow weakening during the first 48 h similar to the previous forecast, then calls for more weakening than previously forecast as the cyclone reaches the colder waters. The initial motion is 315/6. Maria will be moving between the subtropical ridge to the east and a broad trough over the southeastern United States and the adjacent Atlantic waters during the next several days. This pattern should cause the hurricane to turn north-northwestward and then northward during the next 72 h. The track guidance is tightly clustered during this part of the forecast, and the new forecast track is an update of the previous track. After 72 h, the guidance becomes a little more divergent. The Canadian and ECMWF models are on the left side of the envelope showing a generally northward motion, while the GFS is on the right side showing a north-northeastward motion. This part of the forecast track is nudged just a little to the left of the old forecast and the consensus models to account for the ECMWF/Canadian forecasts. KEY MESSAGES: 1. Flash flood warnings continue in portions of Puerto Rico due to persistent heavy rainfall from Maria's trailing rainbands. Everyone in Puerto Rico should continue to follow advice from local officials to avoid these life-threatening flooding conditions. 2. Swells from Maria are expected to begin reaching the coast of the southeastern United States today. These swells are likely to cause dangerous surf and life-threatening rip currents along the coast for the next several days, even with Maria forecast to remain well offshore over the western Atlantic Ocean. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 21.6N 70.6W 110 KT 125 MPH 12H 22/1800Z 22.6N 71.1W 105 KT 120 MPH 24H 23/0600Z 24.2N 71.7W 105 KT 120 MPH 36H 23/1800Z 25.9N 72.2W 100 KT 115 MPH 48H 24/0600Z 27.4N 72.3W 95 KT 110 MPH 72H 25/0600Z 29.5N 72.0W 85 KT 100 MPH 96H 26/0600Z 31.5N 71.0W 75 KT 85 MPH 120H 27/0600Z 33.5N 70.5W 65 KT 75 MPH $$ Forecaster Beven

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Post-Tropical Cyclone Jose Forecast Discussion Number 68

2017-09-22 10:39:40| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Sep 22 2017 000 WTNT42 KNHC 220839 TCDAT2 Post-Tropical Cyclone Jose Discussion Number 68 NWS National Hurricane Center Miami FL AL122017 500 AM AST Fri Sep 22 2017 Since the last advisory, a small burst of deep convection has been observed near the center of Jose. The cyclone is still embedded within a dry environment and located over cold SSTs, so it will be a little surprising if the convection is maintained for an extended period of time this morning. The intensity of the post-tropical cyclone remains 45 kt, based on earlier ASCAT data, and these winds are likely occuring over open water well to the northwest of Jose's center. Surface observations on Martha's Vineyard, Nantucket, and Block Island indicate that tropical storm conditions are still occuring in some locations along the coast. The prior ASCAT pass also showed a wide area of tropical-storm-force winds just offshore of Cape Cod, and there is still some opportunity for these winds to reach the coast this morning. Therefore, the tropical storm warnings remain in effect, and the NHC will continue to issue advisories on Jose. No significant change has been made to the track or intensity forecast. All of the dynamical models remain in good agreement that Jose will remain trapped in weak steering flow while gradually spinning down for the next several days. Although the cyclone has been drifting west for the past 12 hours, a slow turn back toward the east should begin sometime later today and continue through at least day 3. The NHC forecast track is close to the TVCX and HCCA consensus aids. KEY MESSAGES: 1. Tropical-storm-force winds, especially in gusts, are occuring within the tropical storm warning area. These conditions are expected to continue this morning. 2. Minor coastal flooding is possible along portions of the coast of southern New England during the next few days. Please see products issued by local National Weather Service forecast offices. 3. Swells generated by Jose are affecting Bermuda and much of the U.S. east coast, and will likely cause dangerous surf and rip current conditions for the next couple of days in these areas. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 39.7N 68.7W 45 KT 50 MPH...POST-TROPICAL 12H 22/1800Z 39.7N 69.0W 40 KT 45 MPH...POST-TROPICAL 24H 23/0600Z 39.5N 69.0W 40 KT 45 MPH...POST-TROPICAL 36H 23/1800Z 39.2N 68.5W 35 KT 40 MPH...POST-TROPICAL 48H 24/0600Z 38.9N 67.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 25/0600Z 38.5N 67.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/0600Z...DISSIPATED $$ Forecaster Zelinsky

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