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Hurricane Maria Forecast Discussion Number 38

2017-09-25 16:41:08| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Mon Sep 25 2017 000 WTNT45 KNHC 251440 TCDAT5 Hurricane Maria Discussion Number 38 NWS National Hurricane Center Miami FL AL152017 1100 AM EDT Mon Sep 25 2017 Satellite and aircraft data indicate that Maria's structure has changed considerably since yesterday. Deep convection is primarily confined to the eastern semicircle of the circulation and the radius of maximum winds has significantly increased. After not finding many SFMR winds over 60 kt during the overnight flights, the latest Air Force Reserve Aircraft measured SFMR winds of 65-70 kt about 90 n mi from the center over the eastern portion of the circulation. As a result, the initial wind speed is set at 70 kt, a slight readjustment from the 1200 UTC estimate indicated in the intermediate advisory. The 50-kt and 64-kt wind radii have also been adjusted outward primarily over the eastern semicircle based on the aircraft data. The intensity forecast reasoning remains the same as that in the previous advisory. Cool sea surface temperatures, moderate westerly shear, and dry air are expected to cause gradual weakening over the next couple of days. The global model guidance suggests Maria will remain a strong tropical cyclone as it accelerates northeastward later in the forecast period. Therefore, the NHC forecast is a little higher than the statistical guidance at those times. Maria continues to move northward or 360/6 kt. Although Maria is being steered northward between a mid- to upper-level low over the southeastern United States and a subtropical ridge over the southwestern Atlantic, the hurricane's forward motion should remain quite slow as it is currently being impeded by a mid-level ridge over the northeastern United States. A large mid-latitude trough is forecast to move across the Great Lakes region and into the northeast United States by the end of the week. This feature should cause Maria to accelerate east-northeastward to northeastward after 72 hours. The track guidance is in excellent agreement through 48 hours, but there are some differences in Maria's forward speed after that time. The NHC forecast track is near the middle of the guidance envelope through 48 h and is in between the ECMWF and various consensus models later in the period. 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 possible beginning on Tuesday, and a Storm Surge Watch has been issued for portions of eastern North Carolina. 3. Swells from Maria are occurring along the coast of the southeastern United States and will be increasing along the Mid-Atlantic and southern New England coasts today. These swells will likely cause dangerous surf and rip currents at beaches in these areas through much of the week. For more information, please monitor information from your local National Weather Service office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 31.2N 72.9W 70 KT 80 MPH 12H 26/0000Z 31.8N 73.0W 70 KT 80 MPH 24H 26/1200Z 32.9N 73.1W 65 KT 75 MPH 36H 27/0000Z 33.8N 73.1W 65 KT 75 MPH 48H 27/1200Z 34.7N 73.0W 60 KT 70 MPH 72H 28/1200Z 35.7N 71.4W 60 KT 70 MPH 96H 29/1200Z 37.5N 64.5W 60 KT 70 MPH 120H 30/1200Z 42.0N 52.0W 60 KT 70 MPH $$ Forecaster Brown

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Tropical Storm Pilar Forecast Discussion Number 7

2017-09-25 10:57:29| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Mon Sep 25 2017 000 WTPZ43 KNHC 250857 TCDEP3 Tropical Storm Pilar Discussion Number 7 NWS National Hurricane Center Miami FL EP182017 300 AM MDT Mon Sep 25 2017 Although Pilar continues to produce an area of deep convection, surface observations and satellite data indicate that the circulation of the storm is losing definition. In fact, recent ASCAT data suggest that Pilar could already be an open trough. However, we prefer to keep issuing advisories until more confirmation on the structure of the system is available. The initial intensity is held at 35 kt based on the latest Dvorak estimates from TAFB and SAB. Pilar is very near the west coast of Mexico and it is expected to move along or just off the coast during the next day or two. The interaction with land combined with a significant increase in southwesterly shear should cause the cyclone to weaken to a tropical depression later today, and dissipate within the next 24 to 36 hours. Since Pilar lacks a clear center, the initial motion of 340/8 kt is uncertain. A slower north-northwest motion in the low- to mid-level flow is expected until the system dissipates. This track forecast lies closest to the latest GFS model run. The main hazard associated with Pilar is the potential for heavy rainfall, which could cause life-threatening flash floods and mudslides, over the states of Nayarit, the southern portion of Sinaloa, and the southwestern portion of Durango during the next day or so. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 22.2N 106.6W 35 KT 40 MPH 12H 25/1800Z 22.8N 106.8W 30 KT 35 MPH 24H 26/0600Z 23.6N 107.1W 25 KT 30 MPH 36H 26/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Lee Forecast Discussion Number 29

2017-09-25 10:55:00| National Hurricane Center (Atlantic)

Issued at 500 AM AST Mon Sep 25 2017 000 WTNT44 KNHC 250854 TCDAT4 Hurricane Lee Discussion Number 29 NWS National Hurricane Center Miami FL AL142017 500 AM AST Mon Sep 25 2017 Lee continues to hold steady in intensity. The 10 n mi eye of the hurricane remains quite distinct, and although the convective pattern around the eye is fairly symmetric, the cloud tops are not very cold. Since the Dvorak classifications remain the same as earlier, the initial intensity is again held at 80 kt based on a blend of the subjective and objective numbers. It is interesting to note that Lee remains a very compact hurricane, with tropical-storm-force winds extending only 30 n mi from the center. Lee remains in a favorable upper-level wind pattern for strengthening, but SSTs beneath the cyclone are marginal, in part due to the hurricane moving over its own cool wake. Lee is expected to move over slightly warmer waters in a day or so, and that could allow the system to strengthen a little. Later in the forecast period, drier air, a sharp increase in shear, and a track toward colder water should cause weakening. Only minor changes were made to the previous NHC intensity forecast, and this prediction is in best agreement with the consensus models IVCN and HCCA. The trough that had been steering Lee to the east or southeast much of the day on Sunday has now bypassed the system leaving Lee in weak steering currents. A ridge is expected to build to the north of the hurricane by tonight, and that should cause the system to begin moving west-southwestward or westward. By mid-week, a trough is expected to approach the hurricane, and it should cause the system to accelerate to the northeast over the central Atlantic in 4 to 5 days. The NHC track forecast has been adjusted to the west of the previous one to come into better agreement with the latest guidance. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 31.1N 49.4W 80 KT 90 MPH 12H 25/1800Z 30.9N 49.7W 80 KT 90 MPH 24H 26/0600Z 30.7N 50.9W 80 KT 90 MPH 36H 26/1800Z 30.8N 52.4W 85 KT 100 MPH 48H 27/0600Z 31.2N 53.6W 85 KT 100 MPH 72H 28/0600Z 32.7N 54.5W 85 KT 100 MPH 96H 29/0600Z 36.5N 51.5W 75 KT 85 MPH 120H 30/0600Z 42.5N 42.8W 55 KT 65 MPH $$ Forecaster Cangialosi

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Hurricane Maria Forecast Discussion Number 37

2017-09-25 10:51:32| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Sep 25 2017 000 WTNT45 KNHC 250851 TCDAT5 Hurricane Maria Discussion Number 37 NWS National Hurricane Center Miami FL AL152017 500 AM EDT Mon Sep 25 2017 A combination of conventional satellite imagery, scatterometer data, and reports from a NOAA Hurricane Hunter aircraft indicate that Maria is weakening and undergoing major changes in structure as it encounters the cool water left by Hurricane Jose. Satellite imagery shows that the low-level center has become exposed to the northwest of the remaining central convection, with some outer convective banding remaining mainly in the eastern semicircle. The scatterometer and aircraft data suggests that the inner wind core has collapsed, with no hurricane force winds occurring in the western semicircle. Based on the combination of these data, the initial intensity is lowered to a possibly generous 70 kt, and the initial and forecast wind radii have been significantly changed. The initial motion is 355/6. Maria is being steered by the flow between a mid- to upper-level cyclone over the southeastern U.S. and the subtropical ridge over the southwestern Atlantic. A mid-level ridge moving eastward across the northeastern U.S. will likely cause Maria's forward motion to slow some more over the next couple of days. After that time, the mid-latitude westerlies are expected to encroach on Maria, causing it to turn sharply to the east- northeast and accelerate. The guidance is in good agreement on this track scenario, and the new forecast track, which lies between the ECMWF and the various consensus models, is an update of the previous forecast. The environment of cool sea surface temperatures and moderate shear should keep Maria weakening. However, it unclear just how fast it will weaken, as the guidance has been generally forecasting a slower weakening than has actually occurred. The new intensity forecast will follow the trend of the guidance and the previous forecast of a gradual weakening, with Maria now forecast to weaken below hurricane status after 36 h. However, an alternate scenario is that the cyclone continues weakening at a faster rate and thus winds up weaker than the new intensity forecast. Maria is a large cyclone, so even if it weakens to a tropical storm and remains well offshore it is expected to bring tropical storm conditions to portions of the North Carolina coast during the next couple of days. 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 coast beginning Tuesday. A Tropical Storm Warning has been issued for a portion of the coast of North Carolina. 2. Storm surge flooding especially along the sound side of the North Carolina Outer Banks is possible beginning Tuesday, and a Storm Surge Watch has been issued for a portion of the North Carolina Outer Banks. 3. Swells from Maria are increasing along the coast of the southeastern United States and are expected to reach the Mid- Atlantic coast today. These swells will likely cause dangerous surf and rip currents at beaches in these areas through much of the week. For more information, please monitor information from your local National Weather Service office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 30.6N 73.0W 70 KT 80 MPH 12H 25/1800Z 31.4N 73.2W 70 KT 80 MPH 24H 26/0600Z 32.5N 73.3W 65 KT 75 MPH 36H 26/1800Z 33.5N 73.3W 65 KT 75 MPH 48H 27/0600Z 34.3N 73.2W 60 KT 70 MPH 72H 28/0600Z 35.5N 72.0W 60 KT 70 MPH 96H 29/0600Z 37.0N 66.5W 60 KT 70 MPH 120H 30/0600Z 40.0N 56.5W 60 KT 70 MPH $$ Forecaster Beven

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Hurricane Maria Forecast Discussion Number 36

2017-09-25 04:34:44| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sun Sep 24 2017 000 WTNT45 KNHC 250234 TCDAT5 Hurricane Maria Discussion Number 36 NWS National Hurricane Center Miami FL AL152017 1100 PM EDT Sun Sep 24 2017 Hurricane Hunter observations indicate that Maria has weakened. Using a blend of flight-level winds and SFMR-observed surface winds along with a dropsonde in the northeast eyewall of the hurricane, the current intensity is set at 80 kt. Observations from a NOAA aircraft indicate that the SSTs beneath Maria are on the order of 24-25 deg C, which has probably contributed to the decrease of intensity. These relatively cool waters are likely due to mixing and upwelling from slow-moving Hurricane Jose, which traversed the area a little over a week ago. Gradual weakening is anticipated for the next few days, and the official intensity forecast is near or above the latest model consensus. Maria is expected to remain a hurricane for at least the next few days, however. Based on a number of center fixes from the Air Force and NOAA Hurricane Hunters, the motion is northward at a slightly slower speed, or 360/7 kt. Maria is being steered by the flow between a mid-level cyclone near the southeastern U.S. and a subtropical ridge over the southwestern Atlantic. A mid-level ridge over the northeastern U.S. will likely cause Maria's forward motion to slow some more over the next couple of days. The global models predict that this ridge will break down by 72 hours, and this should allow Maria to turn to the right as it begins to approach the mid-latitude westerlies. The official track forecast is similar to the previous one and lies near the left edge of the numerical guidance, in deference to the reliable ECMWF which is the westernmost of the model tracks. Maria is a large hurricane, so it could bring tropical storm conditions to portions of the North Carolina coast in a couple of days, even if its center remains well offshore. 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 coast beginning Tuesday, and a Tropical Storm Watch has been issued for a portion of the coast of North Carolina. 2. Storm surge flooding especially along the sound side of the North Carolina Outer Banks is possible beginning Tuesday, and a Storm Surge Watch has been issued for a portion of the North Carolina Outer Banks. 3. Swells from Maria are increasing along the coast of the southeastern United States and are expected to reach the Mid- Atlantic coast tonight or on Monday. These swells will likely cause dangerous surf and rip currents at beaches in these areas through much of the week. For more information, please monitor information from your local National Weather Service office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 30.0N 73.0W 80 KT 90 MPH 12H 25/1200Z 30.8N 73.2W 80 KT 90 MPH 24H 26/0000Z 31.9N 73.3W 75 KT 85 MPH 36H 26/1200Z 33.0N 73.5W 75 KT 85 MPH 48H 27/0000Z 33.9N 73.5W 70 KT 80 MPH 72H 28/0000Z 35.2N 72.8W 65 KT 75 MPH 96H 29/0000Z 36.5N 69.5W 65 KT 75 MPH 120H 30/0000Z 38.0N 62.0W 65 KT 75 MPH $$ Forecaster Pasch

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