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Tropical Storm Lorenzo Forecast Discussion Number 7
2019-09-24 16:36:36| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Sep 24 2019 000 WTNT43 KNHC 241436 TCDAT3 Tropical Storm Lorenzo Discussion Number 7 NWS National Hurricane Center Miami FL AL132019 1100 AM AST Tue Sep 24 2019 Lorenzo's structure has not changed much during the morning. A small central dense overcast continues over the center with multiple curved bands within the circulation. A recent ASCAT pass showed winds just over 45 kt to the north of the center, but given sampling considerations, the initial intensity remains 55 kt, which matches Dvorak classifications provided by TAFB and SAB. Despite the brief interruption in the strengthening trend, sufficiently warm waters, low shear, and an ambient moist air mass should foster intensification during the next several days. Because Lorenzo has not strengthened further since the previous advisory, the persistence factor has caused the Rapid Intensification (RI) Index (a 25-kt increase in 24 hours) to drop from 53 percent to 23 percent. In addition, the overall guidance envelope is showing slightly lower peak intensities in 3-4 days. The NHC intensity forecast remains near the upper edge of the guidance for much of the forecast period, lying closest to the HWRF and the Florida State Superensemble. RI is still a possibility, but as of yet we have not observed a low-level cyan ring in 37-GHz microwave imagery, which is usually a harbinger of an RI episode. The initial motion remains west-northwestward, or 285/14 kt. Lorenzo is located to the south of a mid-level ridge which extends from Morocco and Madeira Island westward to 40W. Ridging is relatively non-existent west of 40W due to a mid-/upper-level low over the central Atlantic and Tropical Storm Jerry over the western Atlantic. With this pattern in place, Lorenzo is expected begin recurving around the ridge axis over the central Atlantic on days 3-5. During that period, the track guidance envelope is bracketed by the easternmost GFS and westernmost ECMWF models, which are about 350 nm apart on day 5. This spread isn't too significant, and the updated NHC track forecast is only shifted slightly eastward from the previous one, very close to the two corrected consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 12.4N 29.3W 55 KT 65 MPH 12H 25/0000Z 12.9N 31.3W 65 KT 75 MPH 24H 25/1200Z 13.6N 34.0W 75 KT 85 MPH 36H 26/0000Z 14.2N 36.6W 85 KT 100 MPH 48H 26/1200Z 15.0N 38.8W 95 KT 110 MPH 72H 27/1200Z 18.0N 41.9W 100 KT 115 MPH 96H 28/1200Z 21.1N 44.3W 105 KT 120 MPH 120H 29/1200Z 23.9N 45.3W 100 KT 115 MPH $$ Forecaster Berg
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Tropical Storm Lorenzo Forecast Discussion Number 6
2019-09-24 10:55:36| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Sep 24 2019 000 WTNT43 KNHC 240855 TCDAT3 Tropical Storm Lorenzo Discussion Number 6 NWS National Hurricane Center Miami FL AL132019 500 AM AST Tue Sep 24 2019 Satellite images indicate that the cloud pattern associated with Lorenzo continues to become better organized, with many curved bands and a newly formed central dense overcast. In fact, an overnight AMSR2 microwave pass showed that Lorenzo already had a very small central core. The initial wind speed is raised to 55 kt, in accordance with the latest TAFB classification. Conditions seem to be ripe for further intensification given that the storm is over fairly warm waters, with humid mid-level air, and weak/moderate shear. The SHIPS Rapid Intensification index is giving a 53 percent chance of Lorenzo intensifying 25 kt during the next 24 hours, which seems very reasonable since it now has a tight inner core, and after noting the storm just strengthened 25 kt during the previous 24 hours. Thus the intensity forecast is raised from the last one, showing the initial period of very quick strengthening, and is at the upper edge of the guidance. It is worth noting that all of the global models show Lorenzo becoming a fairly large and powerful hurricane within the next 5 days, and the new wind radii forecast reflects this likelihood. The storm is moving west-northwestward at about 14 kt. This general course is expected for the next couple of days while Lorenzo moves beneath the eastern Atlantic subtropical ridge. A break in the ridge should occur in a few days over the central Atlantic, causing the tropical cyclone to turn northwestward and north-northwestward over the weekend. The new forecast is shifted slightly northward in the short term, but is close to the previous NHC prediction thereafter, closest to the corrected-consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 12.0N 28.0W 55 KT 65 MPH 12H 24/1800Z 12.6N 30.0W 65 KT 75 MPH 24H 25/0600Z 13.3N 32.7W 80 KT 90 MPH 36H 25/1800Z 13.9N 35.5W 90 KT 105 MPH 48H 26/0600Z 14.4N 38.0W 95 KT 110 MPH 72H 27/0600Z 17.0N 41.7W 100 KT 115 MPH 96H 28/0600Z 20.0N 44.5W 105 KT 120 MPH 120H 29/0600Z 23.0N 46.0W 105 KT 120 MPH $$ Forecaster Blake
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Tropical Storm Karen Forecast Discussion Number 9
2019-09-24 10:51:32| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Sep 24 2019 000 WTNT42 KNHC 240851 TCDAT2 Tropical Storm Karen Discussion Number 9 NWS National Hurricane Center Miami FL AL122019 500 AM AST Tue Sep 24 2019 During the last pass through Karen's center around 0430 UTC, the Air Force reconnaissance aircraft reported some believable SFMR winds of 34-35 kt in the southeastern quadrant and an extrapolated central pressure of 1006 mb. The 925-mb flight-level height had also decreased by almost 20 meters in about 2 hours, an indication that the lower pressure estimate was legitimate. Reflectivity and velocity data from the San Juan NOAA WSR-88D Doppler radar also enunciate that Karen's inner-core has become better defined over the past few hours. Satellite intensity estimates at 0600 UTC were T2.5/35 kt from TAFB, and T2.4/34 kt and 40 kt from UW-CIMSS ADT and SATCON, respectively. Based on the recon and satellite intensity data, Karen has re-strengthened to tropical storm status. The initial motion is now northward or 360/06 kt. Karen's forecast track hinges heavily on the future intensity and associated vertical structure of the cyclone. The GFS, GFS-Legacy, UKMET, and HRWF dynamical models take a much weaker and more vertically shallow cyclone northeastward after 48 hours and either continue with that motion through day 5 or dissipate the system. In contrast, the ECMWF and many of its stronger ensemble members stall Karen around days 3-4 and then turn the somewhat stronger and deeper cyclone westward to west-southwestward to the south of a building ridge. Given that Karen is forecast to be stronger and vertically deeper than the weaker models, the current track forecast leans more toward the stronger ECMWF and ECMWF-Ensemble model solutions. The new NHC forecast is to the right of the previous advisory track and slower, especially on days 3-5, but the new track does not extend as far east as the weaker GFS, UKMET, and HWRF models or the consensus models that incorporate those three models. None of the dynamical models, including the HWRF and HMON hurricane models, show much in the way of strengthening once Karen moves north of Puerto Rico and Virgin Islands except for the ECMWF model, despite the very low vertical wind shear conditions that the cyclone will be moving into by 24 hours and beyond. Given Karen's decent wind field and vertical structure, the expected low shear conditions, moist mid-level environment, and SSTs of more than 29 deg C for the next 48 hours or so, forecasting at least slow but steady strengthening seems to be quite reasonable. By days 3-5, the mid-level environment dries out significantly, which the weaker models seem to be keying on. However, if Karen strengthens as currently expected, then the cyclone's robust circulation should be able to mix out any dry air intrusions, allowing for at least additional modest intensification to occur in the 72-120 hour period. The official intensity forecast is a little above the previous advisory, and is basically an average of the weaker dynamical models and the stronger GFS- and ECMWF-based statistical-dynamical models Decay-SHIPS and LGEM. Key Messages: 1. Karen is expected to bring heavy rainfall, flash floods and mudslides to Puerto Rico and the U.S. and British Virgin Islands today, where a tropical storm warning is in effect. The rainfall and potential flooding will likely continue on Wednesday even as the center of Karen moves away from Puerto Rico and the Virgin Islands. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 16.8N 65.8W 35 KT 40 MPH 12H 24/1800Z 18.1N 65.9W 35 KT 40 MPH 24H 25/0600Z 20.1N 65.5W 40 KT 45 MPH 36H 25/1800Z 22.6N 64.7W 45 KT 50 MPH 48H 26/0600Z 24.6N 64.0W 50 KT 60 MPH 72H 27/0600Z 27.3N 62.7W 55 KT 65 MPH 96H 28/0600Z 28.0N 63.0W 60 KT 70 MPH 120H 29/0600Z 27.7N 65.5W 60 KT 70 MPH $$ Forecaster Stewart
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Tropical Storm Kiko Forecast Discussion Number 48
2019-09-24 10:43:07| National Hurricane Center (East Pacific)
Issued at 1100 PM HST Mon Sep 23 2019 000 WTPZ43 KNHC 240842 TCDEP3 Tropical Storm Kiko Discussion Number 48 NWS National Hurricane Center Miami FL EP132019 1100 PM HST Mon Sep 23 2019 Satellite and microwave data indicate that the center of Kiko is no longer in the middle of the central dense overcast. Instead, increasing shear has caused the low-level center to be displaced to the southwestern edge of the deep convection. Intensity estimates are decreasing, and the initial wind speed is set to 45 kt, which agrees best with recent 40-45 kt ASCAT data. Kiko is moving northwestward at 9 kt. The storm is expected to turn to the west-northwest on Tuesday in the flow between a mid-level ridge to the northeast and a mid- to upper-level low to the west. By Wednesday, Kiko is expected to turn back to the west and eventually south-of-west as the shallower system is steered by the low-level trade winds. The new track forecast is similar to the previous one, except adjusted southward on days 2-3. The storm should continue to weaken over the next few days due to persistent south-southwest shear, marginal water temperatures, and a dry mid-level environment. Guidance tonight has accelerated the transition into a non-convective remnant low, with everything now showing post-tropical status by 48 hours. The new forecast is lower than the previous one, following the trend in the models, and could be too slow in showing the storm's demise. Still, Kiko has been one for the record books and should enter the top 10 in longest-lived eastern Pacific tropical cyclones by midday Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 17.5N 138.2W 45 KT 50 MPH 12H 24/1800Z 18.5N 139.3W 35 KT 40 MPH 24H 25/0600Z 19.4N 140.8W 30 KT 35 MPH 36H 25/1800Z 19.7N 142.1W 25 KT 30 MPH 48H 26/0600Z 19.5N 143.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 27/0600Z 18.5N 145.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 28/0600Z...DISSIPATED $$ Forecaster Blake
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Tropical Storm Jerry Forecast Discussion Number 28
2019-09-24 10:31:04| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Sep 24 2019 000 WTNT45 KNHC 240830 TCDAT5 Tropical Storm Jerry Discussion Number 28 NWS National Hurricane Center Miami FL AL102019 500 AM AST Tue Sep 24 2019 Conventional satellite imagery and a series of recent microwave images show that Jerry's cloud pattern has begun to deteriorate. Diminishing deep convection is now confined to the north portion of the cyclone. A blend of the subjective and objective satellite intensity estimates from TAFB, SAB, and UW-CIMSS respectively, support decreasing the initial intensity to 50 kt. Strong vertical shear and an intruding dry, stable thermodynamic atmosphere associated with a high amplitude mid- to upper-level trough moving off of the east coast of the U.S. is finally taking its toll on Jerry. Weakening has begun, and the statistical- dynamical intensity guidance, as well as the large-scale deterministic models show the aforementioned inhibiting environment persisting through the entire 5 day period. Consequently, further weakening is expected, and Jerry should degenerate into a remnant low in 4 days, with dissipation occuring over the weekend, and this scenario is consistent with global model forecasts. The initial motion is estimated to be northward, or 360/7 kt. Jerry will continue moving within a large break in the subtropical ridge through most of today, then turn northeastward later tonight within the mid-tropospheric southwesterly flow produced by the previously mentioned approaching trough. Around mid-period, Jerry should move east-northeastward within the deep-layer mid-latitude zonal flow, then a little to the south of east in the peripheral flow of the subtropical high anchored to the southwest of the cyclone. The NHC track forecast is somewhat slower beyond the 24 hour period than the previous advisory to align more with the reliable TVCA multi-model consensus. Wind radii were adjusted based on 0150 UTC MetOp scatterometer data, and the forecast wind radii for the 24 and 36 hour periods are based on the global and regional model RVCN consensus. Key Messages: 1. Tropical-storm-force winds are expected on Bermuda later today. Large swells are also expected to affect the coast of Bermuda during the next few days. These swells could cause life-threatening rip currents. See products issued by the Bermuda Weather Service for more information. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 29.8N 68.4W 50 KT 60 MPH 12H 24/1800Z 30.6N 68.4W 45 KT 50 MPH 24H 25/0600Z 31.7N 67.0W 40 KT 45 MPH 36H 25/1800Z 32.7N 64.6W 35 KT 40 MPH 48H 26/0600Z 33.6N 61.9W 30 KT 35 MPH 72H 27/0600Z 34.9N 56.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 28/0600Z 35.0N 54.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 29/0600Z...DISSIPATED $$ Forecaster Roberts
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