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Tropical Storm Lee Forecast Discussion Number 7

2017-09-16 16:59:55| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 16 2017 000 WTNT44 KNHC 161459 CCA TCDAT4 Tropical Storm Lee Discussion Number 7...Corrected NWS National Hurricane Center Miami FL AL142017 1100 AM AST Sat Sep 16 2017 Corrected to include missing word in intensity discussion Deep convection has increased in intensity and coverage since this time yesterday, and a recent partial ASCAT pass from around 1100 UTC indicated that the system is now producing tropical-storm-force winds at least to the east of its center. Based on these data, the depression is upgraded to Tropical Storm Lee with maximum winds of 35 kt. Lee has been able to strengthen a little despite about 15 kt of north-northwesterly shear. The cyclone appears to be located in a sweet spot of relatively low shear, with much stronger upper- level westerly winds located not too far to the north, and it may be able to thread the needle of lower shear for another 36 hours or so. After that time, the westerlies drop southward, and Lee will likely be hammered by 30 kt of westerly shear by 48 hours. With all that in mind, Lee is forecast to strengthen only slightly over the next day or so, with weakening expected to begin by day 3. The NHC intensity forecast is close to the intensity consensus and HCCA, and Lee may ultimately degenerate into a remnant low by day 5. Lee's initial motion is estimated to be 265/10 kt. The storm is located to the south of a weak mid-level ridge, and it is expected to move generally westward or west-northwestward for the entire forecast period. Although some of the track models are showing a more pronounced poleward motion, Lee's relatively low intensity and eventual weakening will likely keep it steered by lower-level flow. As a result, the NHC track forecast is near the southern edge of the guidance envelope, although not quite as far south as the ECMWF model. This forecast is not too different from the previous one. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 12.5N 33.1W 35 KT 40 MPH 12H 17/0000Z 12.4N 34.1W 40 KT 45 MPH 24H 17/1200Z 12.5N 35.3W 40 KT 45 MPH 36H 18/0000Z 12.9N 36.7W 40 KT 45 MPH 48H 18/1200Z 13.6N 38.4W 40 KT 45 MPH 72H 19/1200Z 15.6N 42.3W 35 KT 40 MPH 96H 20/1200Z 17.0N 46.0W 30 KT 35 MPH 120H 21/1200Z 18.0N 49.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

Tags: number discussion lee storm

 

Potential Tropical Cyclone Fifteen Forecast Discussion Number 1

2017-09-16 16:51:26| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 16 2017 000 WTNT45 KNHC 161451 TCDAT5 Potential Tropical Cyclone Fifteen Discussion Number 1 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Sat Sep 16 2017 Satellite images indicate that the area of low pressure located several hundred miles east of the Lesser Antilles has become better organized with curved banding features now better established. Since there is still no indication of a well-defined center and because tropical storm watches have been issued for portions of the Leeward Islands, NHC has initiated advisories on this system as a potential tropical cyclone. The initial wind speed is estimated to be 30 kt based on a blend of the Dvorak classifications from TAFB and SAB. The initial motion estimate is 280/19, but this is uncertain due to the lack of a clear center. A slower west-northwestward motion is expected during the next several days as a mid-level ridge to the north of the system weakens but remains nearly stationary. The NHC track forecast takes the system across the Leeward Islands in a few days and then near the Virgin Islands and Puerto Rico by the end of the forecast period. It should be noted that confidence in the track and forward speed of this system is low due to the spread in the models and the current lack of a well-defined center. The disturbance is expected to be in environmental conditions conducive for strengthening during the next several days as the shear is expected to be 10 kt or less while the cyclone moves over warm 29 deg C SSTs. These conditions should allow for at least steady strengthening, and the models unanimously show that trend. The NHC intensity forecast is conservative for now, but does show the system becoming a tropical storm later today and a hurricane by the time it reaches the Leeward Islands. KEY MESSAGES: 1. The disturbance is expected to intensify and will likely bring tropical storm and hurricane conditions as well as flooding rainfall to portions of the Lesser Antilles early next week. These conditions could also spread into the Virgin Islands and Puerto Rico by mid week. Interests in these areas should monitor the progress of this system and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 12.2N 50.5W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 17/0000Z 12.8N 52.8W 35 KT 40 MPH...TROPICAL STORM 24H 17/1200Z 13.6N 55.1W 40 KT 45 MPH 36H 18/0000Z 14.3N 56.9W 50 KT 60 MPH 48H 18/1200Z 15.0N 58.6W 60 KT 70 MPH 72H 19/1200Z 16.3N 61.3W 75 KT 85 MPH 96H 20/1200Z 17.6N 64.0W 80 KT 90 MPH 120H 21/1200Z 18.7N 67.3W 80 KT 90 MPH $$ Forecaster Cangialosi

Tags: number discussion potential tropical

 
 

Hurricane Jose Forecast Discussion Number 45

2017-09-16 16:42:25| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sat Sep 16 2017 000 WTNT42 KNHC 161442 TCDAT2 Hurricane Jose Discussion Number 45 NWS National Hurricane Center Miami FL AL122017 1100 AM EDT Sat Sep 16 2017 Earlier microwave data seemed to suggest that Jose's low-level center is displaced to the northwest of the mid-level microwave eye, which is not surprising given that the various shear analyses indicate about 25 kt from the west-northwest. The initial intensity is being held at 70 kt, pending the arrival of an Air Force Reserve Hurricane Hunter aircraft this afternoon. The shear over Jose is not expected to abate, and in fact, it could increase further in the next 36 to 48 hours. However, the hurricane will remain over warm waters south of the Gulf Stream for the next three days, and the intensity models suggest that it should be able to at least maintain its intensity, if not strengthen slightly. After day 3, the hurricane will move north of the Gulf Stream over much colder water, and that will likely lead to the system weakening to a tropical storm. Although there will be a cold front approaching from the northwest by day 5, Jose still looks separated from the frontal zone at that point, and there is no appreciable injection of baroclinic energy at that time to allow for strengthening. Best I can tell, Jose is moving northwestward with an initial motion of 320/8 kt. Jose will be moving around the western periphery of a mid-level high anchored to the east of Bermuda, which will cause it to turn northward and maintain that heading through day 3. The track models are tightly clustered during this period, and there is relatively high confidence in the NHC forecast. After day 3, the models have come into much better agreement that Jose will become embedded in the mid-latitude westerlies, and the NHC track forecast is faster than the previous one by day 5 in order to keep up with the GFS and ECMWF. Regardless, Jose's track and an expected increase in size will likely lead to impacts along the mid-Atlantic and southern New England coasts in a few days. KEY MESSAGES: 1. The center of Jose is forecast to pass well east of the North Carolina coast on Monday, and tropical-storm-force winds are currently expected to remain offshore of the North Carolina Outer Banks. However, an increase in the size of the storm or a westward adjustment in the track forecast could bring tropical storm conditions closer to the Outer Banks, and interests there should monitor the progress of Jose through Monday. 2. While Jose is currently forecast to remain offshore of the U.S. coast from Virginia northward to New England, the large cyclone could cause some direct impacts to these areas and any deviation to the left of the NHC forecast track would increase the likelihood and magnitude of those impacts. Interests along the U.S. east coast from Virginia to New England should monitor the progress of Jose through the next several days. 3. Swells generated by Jose are affecting Bermuda, the Bahamas, the northern coasts of Hispaniola and Puerto Rico, and much of the U.S. east coast. These swells are likely to cause dangerous surf and rip current conditions for the next several days in these areas. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 28.8N 72.2W 70 KT 80 MPH 12H 17/0000Z 29.5N 72.4W 75 KT 85 MPH 24H 17/1200Z 30.8N 72.2W 75 KT 85 MPH 36H 18/0000Z 32.4N 72.0W 75 KT 85 MPH 48H 18/1200Z 34.0N 72.0W 70 KT 80 MPH 72H 19/1200Z 37.2N 71.5W 65 KT 75 MPH 96H 20/1200Z 40.5N 69.5W 60 KT 70 MPH 120H 21/1200Z 41.5N 63.5W 50 KT 60 MPH $$ Forecaster Berg

Tags: number discussion jose forecast

 

Tropical Depression Fifteen-E Forecast Discussion Number 20

2017-09-16 16:39:58| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Sep 16 2017 000 WTPZ45 KNHC 161439 TCDEP5 Tropical Depression Fifteen-E Discussion Number 20 NWS National Hurricane Center Miami FL EP152017 800 AM PDT Sat Sep 16 2017 Deep convection associated with the depression has increased this morning, with the low-level center estimated to be near the middle of the thunderstorm activity. Based on the improved organization of the cloud pattern since the time of the ASCAT pass overnight, the initial wind speed is nudged upward to 30 kt. The depression is over relatively warm SSTs and embedded in fairly low wind shear conditions, but it also is situated in a dry atmospheric environment. These mixed factors should cause the system to remain relatively steady state for the next few days, though it is possible that the cyclone becomes a tropical storm during that time frame. Beyond a few days, the wind shear is expected to increase and SSTs lower along the expected path. These more hostile conditions should cause the depression to weaken and become a remnant low in 4 to 5 days. The NHC intensity forecast is an update of the previous one, and in line with the bulk of the guidance. The tropical cyclone continues to drift westward in weak steering currents. The models are in agreement that the depression should turn slowly northward during the next day or two when it moves along the west side of a weak mid-level ridge. Once the system loses convection, a turn back toward the west is predicted. Only minor changes were made to the previous NHC track forecast. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 15.8N 126.5W 30 KT 35 MPH 12H 17/0000Z 15.9N 126.8W 30 KT 35 MPH 24H 17/1200Z 16.3N 127.0W 30 KT 35 MPH 36H 18/0000Z 16.9N 127.0W 30 KT 35 MPH 48H 18/1200Z 17.6N 127.0W 30 KT 35 MPH 72H 19/1200Z 18.2N 127.5W 30 KT 35 MPH 96H 20/1200Z 17.8N 129.2W 25 KT 30 MPH 120H 21/1200Z 16.7N 132.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

Tags: number discussion tropical depression

 

Hurricane Norma Forecast Discussion Number 9

2017-09-16 16:37:52| Tropical Depression LIDIA

Issued at 900 AM MDT Sat Sep 16 2017

Tags: number discussion forecast norma

 

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