Issued at 300 AM GMT Fri Oct 10 2025
000 WTNT41 KNHC 100251 TCDAT1 Subtropical Storm Karen Discussion Number 1 NWS National Hurricane Center Miami FL AL112025 300 AM GMT Fri Oct 10 2025 Over the last 12-18 hours, NHC has been monitoring a small area of low pressure (AL96) embedded in a much larger upper-level trough, located about 400 n mi to the northwest of the northernmost Azores Islands. The system was originally a frontal low that quickly became occluded early on 8 October. Since that time, the low has been gradually shedding its remaining frontal features as shallow to moderate convection formed near the center. Earlier today, there was a Sentinel-1A Synthetic Aperture Radar (SAR) pass that indicated the system no longer was attached to frontal boundaries and had a contracted radius of maximum wind of 20 n mi. Since that time, the convective cloud tops have cooled to -50 to -55 C around the center, with a distinct warm spot seen near the center. A recent WSFM microwave pass also indicated a nearly closed cyan ring on the 37-GHz channel. 00 UTC subjective satellite classifications on the system were a ST1.5/25-30 kt from TAFB, and a T3.0/45 kt from SAB. A blend of all of these various data points indicate that the system has made the transition to Subtropical Storm Karen. The initial intensity is set at 40 kt, in agreement with a recently received scatterometer pass which had a peak wind of 38 kt. This also matches the special 02 UTC fix of ST 2.5/35-40 kt received from TAFB. The subtropical storm is moving slowly northeastward, estimated at 050/8 kt. Karen is already well established in the mid-latitude westerlies for being at such a high latitude, and is likely to be caught up by another mid-latitude trough that is digging in from the west. The track guidance in in pretty good agreement on a northeastward motion with a gradual acceleration over the next 24-36 hours, and the NHC track forecast is roughly in the middle of the guidance envelope, close to the simple and corrected consensus aids. While Karen has made the transition to a subtropical storm, it still remains fully embedded in a large upper-level low, so large in fact that it has helped the shear over the system remain fairly low and has enabled the convection to coalesce near the center. Very cold upper-level temperatures also appear to be contributing to the convective vigor, allowing cloud tops of -50 C to persist near the center. However, even colder sea-surface temperatures lie ahead of Karen's path, and it seems like the system only has about a day or so before it is quickly overtaken by the next mid-latitude trough. The global models show the small cyclone opening up into a trough by 48 h, and it is also possible the system could become post-tropical before then if it loses its current organized convection. This intensity forecast is in general agreement with the mean of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 44.5N 33.0W 40 KT 45 MPH 12H 10/1200Z 45.6N 31.7W 40 KT 45 MPH 24H 11/0000Z 47.8N 29.5W 40 KT 45 MPH 36H 11/1200Z 50.6N 28.0W 35 KT 40 MPH 48H 12/0000Z...DISSIPATED $$ Forecaster Papin
NHC Atlantic
